Process for the production of metal melts

ABSTRACT

To be able to produce metal melts using any metal carriers incurring in metallurgical practice as the charging materials, namely in the most diverse quantitative compositions, a plant for producing metal melts is provided with the following characteristic features:  
     an electric arc furnace vessel ( 1 ) provided with one charging opening ( 11, 21 ) for a metal melt and/or scrap and/or direct educed metal, in particular direct reduced iron, and/or ore and at least one electrode ( 16 ) and one slag tapping means ( 22 ),  
     an oxygen-blowing converter vessel ( 3 ) provided with one melt tapping means ( 41 ),  
     wherein the oxygen-blowing converter vessel ( 3 ) and the electric arc furnace vessel ( 1 ) form a unit which is connected via an overflow weir ( 34 ) and which is rigidly mounted on the foundation and,  
     wherein the bath surface related specifically to the bath volume is smaller in the oxygen-blowing converter vessel ( 3 ) than in the electric arc furnace vessel ( 1 ) and  
     the oxygen-blowing converter vessel ( 3 ) shares a common reaction space with the electric arc furnace vessel ( 1 ), which space is arranged above the bath level of these vessels.

[0001] This is a division of application Ser. No. 09/258,755 filed Feb.26, 1999, which is a continuation application of InternationalApplication PCT/AT98/00160 having an international filing date of Jun.26, 1998.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a plant for the production of metalmelts, in particular iron melts, such as steel melts, crude steel meltsor pig iron melts, and a process for the production of these melts.

[0004] 2. Description of the Related Art

[0005] The present standard aggregate used for the production ofelectric steel is an a.c. or d.c. electric arc furnace. The ironcarriers charged, which are comprised of

[0006] 60 to 100% steel scrap, directly reduced iron-sponge iron invarious quantitative ratios and sometimes also iron carbide (at present,up to about 10 to 20% of the total charge), and

[0007] 0 to 40% liquid and/or solid pig iron

[0008] are melted by aid of one or several electric arcs using oxygenlance(s)—if desired, burner(s), nozzles and/or inert gas flushing—andunder the addition of carbon carriers and slag formers. After this, thesteel bath during a flat bath period (5 to 10 min) in an electric arcfurnace is brought to the temperature and composition desired fortapping and is killed in the ladle during tapping. Energy and materialconsumption as well as plant productivity vary greatly as a function ofthe respective charging ratios and melting practice.

[0009] Due to world-wide introduction of secondary metallurgicalprocesses as well as a series of developments on the constructive,electric and technological sectors, electric arc furnace melting haschanged within the past few years into a process both flexible andefficient in terms of charging substances and steel quality produced,more and more exhibiting substantial advantages over convertermetallurgy and competing the same successfully. With new processdevelopments, important reductions of the melting time and the specificelectric energy consumption and hence further reduction of the specificoperating and investment costs of electric steel production in electricarc furnaces have been attained primarily by applying

[0010] integrated scrap preheating and/or hot charging of spongeiron/hot briquetted directly reduced iron

[0011] continuous addition of a major portion of the charging substances(iron carriers, carbon carriers, fluxes, etc.) while minimizing thepower-off time for carrying out charging operations

[0012] optimum foamed slag operation and

[0013] cheaper primary energies (coal, natural gas, etc.) as asubstitute for electric energy, including an improvedoffgas-afterburning operation and more efficient utilization of heat.

[0014] However, with the known processes for the production of electricsteel by means of electric arc furnaces used as melting aggregates, thepotential advantages of the above-mentioned process developments havebeen utilized to a limited extent only. Moreover, it has not beenfeasible so far—despite an increasing demand—to process to liquid steelhigh portions of liquid pig iron and/or other carbon-rich iron carriers(sponge iron, iron carbide etc.) as well as problem scrap (used cars) ofabout 30 to 70% charged into electric arc furnaces, at a highproductivity and energy utilization and, with car scrap, also withoutinadmissible loads on the environment. The commercial application of atechnology and plant based on electric arc furnace technology and highlyefficient under such conditions from an economic point of view is stillwanting.

[0015] The above-mentioned limitations with conventional electric arcfurnaces are due exclusively to the configuration of the furnaces, whichdoes not enable a quasi-stationary continuous process course. Theoperations of charging, melting, refining, heating and tapping takeplace on one site, by necessity more or less offset in time and withinterruption(s) of the charge and current supply—at least before andafter tapping—in order to obtain the desired composition and temperature(homogeneity and overheating in respect of the liquidus temperature) ofthe crude steel. The present process course in an electric arc furnaceis discontinuous and hence limited in its performance. In this respect,the following is noted:

[0016] 1. With already reached tap-to-tap times of ≦55 min withconventional electric arc furnaces and ≦5 min for electric arc furnaceswith shaft, respectively, for tap weights of 70 to 150 tons, thepossibility of further reducing the power-off phases is stronglylimited. The same holds for the power-on phases—since under suchconditions the limits for an economic energy input per ton of charge andtime unit—and hence for the overall melting time have almost beenreached.

[0017] 2. In continuous charging as well as in refining and heating inthe flat bath operation, which will take a substantially longer timewith high charging portions of sponge iron and, in particular, of liquidpig iron and iron carbide (about 6.1% C), thus also increasing the heatloss, the actual transformer output, as a rule, is not completelyutilized by electric arc furnaces.

[0018] From AT-B-295,566 a process for the continuous production ofsteel by melting, prereduced ore and subsequently refining the melt ofsemi-steel to steel in an electric arc melting furnace comprising amelting hearth to which a refining zone and at least one slag depositingchamber are connected is known, in which prereduced iron ore isintroduced into the electric arc zone of the melting hearth in a lumpyor granular form, the metal is continuously agitated and set in acirculatory movement within the hearth and the metal is refined to steelwhile flowing through a refining zone by blowing in an oxygen-containinggas, whereas slag is caused to stream opposite to the metal at leastalong part of the length of the refining zone. The slag calms down in aslag depositing chamber without intensive mixing of the bath and then istapped from the slag depositing chamber.

[0019] In that known process, plant scrap and liquid pig iron may becharged, yet each in very limited amounts only. Discharging of theoffgases takes place directly in the refining zone, i.e., not via theelectric arc melting furnace. The refining zone is constructed as achannel-type reactor, resulting in a high specific surface area withhigh heat losses. Refining is carried out with a C-concentrationgradient along the refining zone of the channel-type reactor without aconcentration balancing tank, and therefore the C content is difficultto adjust or control. Consequently, that known process is applicable toa limited extent only, in the first place serving to produce crude steelfrom prereduced ore.

[0020] From DE-C 3 609 923 a process and an arrangement for continuouslymelting scrap to crude steel is known. In that process, which primarilyis limited to scrap melting (no mention being made of charging liquidpig iron and/or sponge iron), the heat of the furnace gases is utilizedor heating the scrap. The scrap is preheated in a shaft centrally placedon the hearth-type furnace and is introduced centrally into thehearth-type furnace, thereby forming a scrap column supported on thebottom of the electric arc furnace under formation of a conical pile andcapable of reaching up as far as to the scrap charging opening providedin the upper part of the scrap preheating shaft. Pivotable electrodes(preferably four electrodes) are symmetrically arranged about the scrapcolumn in the electric arc furnace and assist in melting the scrap. Theangle of inclination between the central axis of an electrode and avertical line during scrap melting amounts to more than 20° for each ofthe electrodes. Thereby, the hearth-type furnace is exposed to a greatthermal load, since the electric arcs are burning between the centrallyintroduced scrap column and the walls and lid of the hearth-typefurnace. On the one hand, this causes an increased wear of therefractory lining and hence elevated material and time costs for doingrepairs. In addition, a large portion of the input energy is imparted byradiation to the furnace walls and the furnace lid and thereby getslost. Moreover, possible bridging within the scrap column—above the meltcaverns melted into it by the electrodes—may cause precipitation of thescrap column (or parts thereof), which might lead to a break of theelectrodes and hence interrupt the process.

[0021] From MPT International 2/1996, pages 56 to 60, the Contiarcprocess is known in which scrap is melted continuously, namely in anannular shaft furnace. This process serves exclusively for the meltingof scrap; charging of sponge iron and/or liquid pig iron are notmentioned at all. One disadvantage associated with this method are thedifficulties in adjusting the crude steel temperature immediately beforestarting and while performing the tapping operation, since there is avery large contact area of the scrap, which is arranged in the shape ofa ring, with the liquid bath. There may also arise difficulties inrespect of the balancing out of concentrations or in respect of thechemical homogeneity of the melt which is refined and tappeddiscontinuously with this process.

[0022] According to the Consteel® process (known from Electric FurnaceConference Proceedings 1992, pp. 309 to 313), scrap is preheated usingan elongated horizontal preheating furnace and is charged to an electricfurnace, namely at one side of the electric furnace. The offgas arisingin the electric furnace is carried off via the elongated preheater forthe scrap. However, no optimum gas utilization results in this process,since the scrap is not streamed through by the offgas but the latteronly passes across the same. The elongated preheating channel for thescrap is stationarily arranged, whereas the electric furnace is mountedso as to be tiltable in order to enable a crude steel tapping operationwhich is discontinuous with this process. The structure as such is thusexpensive, as with all pivotable furnaces. There results mechanical wearof the refractory furnace lining. Charging of the scrap isdiscontinuous, since the scrap is introduced on one side of the furnaceonly, namely is deposited in a marginal region of the furnace. As aresult, the melting and mixing operations cannot be carried out in anoptimum manner, and in using burners in the electric furnace to supportmelting of the scrap only a low efficiency would be achieved. Thecontent of dust in the offgas is relatively large since scrap is notfiltered off from the offgas.

SUMMARY OF THE INVENTION

[0023] The invention aims at avoiding these drawbacks and difficultiesand has as its object to provide a plant as well as a process forproducing metal melts, in particular iron melts, which basically enablethe charging of any metal carriers incurring in metallurgical practice,preferably iron carriers having various physico-chemical properties,such as iron scrap, liquid and/or solid pig iron, iron carbide, spongeiron, iron ore having different degrees of prereduction, sinter, scales,metallurgical dust, dried sludges, etc., in various quantativecompositions such that, for instance, if there is a shortage of one ironcarrier another one may be used instead without capacity restrictions.

[0024] To achieve this object, a plant according to the invention isprovided with the following characteristic features: comprising

[0025] an electric arc furnace vessel provided with at least onecharging opening for a metal melt and/or scrap and/or direct reducedmetal, in particular direct reduced iron, and/or ore and at least oneelectrode as well as at least one slag tapping means,

[0026] an oxygen-blowing converter vessel provided with at least onemetal tapping means, wherein

[0027] the oxygen-blowing converter vessel and the electric arc furnacevessel form a unit which is connected via an overflow weir, and

[0028] the bath surface related specifically to the bath volume issmaller in the oxygen-blowing converter vessel than in the electric arcfurnace vessel and

[0029] the oxygen-blowing converter vessel shares a common reactionspace with the electric arc furnace vessel, which space is arrangedabove the oath level of these vessels.

[0030] The plant in accordance with the invention in addition to solvingthe problem defined above offers the advantage that in case ofcontinuous tapping the refractory lining of the plant parts is subjectedto no and in case of discontinuous tapping only to slight strainsresulting from changes in temperature.

[0031] Due to the unit composed of the converter vessel and the electricarc furnace vessel being preferably rigidly arranged with respect to thefoundation there is no mechanical load on the vessels, in particular therefractory lining thereof, by tilting movements or by any weight shiftsresulting therefrom. In addition, the refractory brick-lining inside theelectric arc furnace vessel will be protected since, in that vessel, ametal melt rich in C at all times exerts a reducing effect on the slagor lowers the content of FeO in the slag, respectively. The temperaturewithin the electric arc furnace vessel is relatively low, namely lowerthan 1600° C.

[0032] For an optimum refining operation in the oxygen-blowing convertervessel it is of advantage if the tapping-level of the metal bath of theoxygen-blowing converter vessel is located below the level of the metalbath of the electric arc furnace vessel, wherein the bottom of theoxygen-blowing converter vessel is advantageously arranged on a lowerlevel than the bottom of the electric arc furnace vessel.

[0033] Preferably, the oxygen-blowing converter vessel is provided withone blowing lance for oxygen or an oxygen-containing gas mixture.

[0034] According to a preferred variant, the oxygen-blowing convertervessel is provided with bottom nozzles, preferably with oxygen-blowingbottom nozzles.

[0035] Advantageously, the electric arc furnace vessel is provided withat least one metal tapping means.

[0036] Suitably, the slag tapping means is provided on a decantingvessel which forms a unit with the electric arc furnace vessel, whichdecanting vessel is preferably arranged so as to be locateddiametrically opposite the overflow weir. Hereby it feasible to make theslag forming in the oxygen-blowing converter vessel flow into theelectric arc furnace vessel in counterflow to the metal melt.

[0037] Suitably, the oxygen-blowing converter vessel and/or the electricarc furnace vessel is/are provided with a charging opening for chargingmetallic charging substances, ore, fluxes. alloys, carburizing agentsand, further, the oxygen-blowing converter vessel is provided withafterburning nozzles and/or lances feeding an oxygen-containing gas oroxygen, preferably at least one thereof in the vicinity of thetransition between the two vessels.

[0038] According to a preferred embodiment, the electric arc furnacevessel is provided with at least one preheating shaft supplying solidiron carriers which is arranged above the electric arc furnace vesseland preferably at the side thereof or annularly above the furnacevessel, thus enabling preheated scrap and/or sponge iron or other ironcarriers to be charged in a simple manner and while utilizing the heatcontent of the offgases arising in the electric arc furnace vessel. Thepreheating shaft may be arranged centrally or at a de-centralizedposition and preferably is not provided with gas-permeable shut-offdevices (fingers), i.e. the preheating shaft discharges into theelectric arc furnace vessel directly and without any obstacles, with thesolid iron carriers forming a column having its base on the bottom ofthe electric arc furnace vessel.

[0039] According to another preferred embodiment, at least one conveyorbelt being preferably provided with a casing enters the preheatingshaft, wherein, suitably, the casing is entered by heating means mountedin the casing and configured as afterburning means and/or burners havingducts feeding an oxygen-containing gas.

[0040] For efficient use of the supplied energy advantageously at leastpart of the inner surface of the preheating shaft and/or the casingand/or the lid of the electric arc furnace vessel and/or the lid of theoxygen-blowing converter vessel is lined with refractory materials.

[0041] Preferably the electric arc furnace vessel is provided with ameans for feeding a metal melt, preferably pig iron.

[0042] According to an alternative variant, the electric arc furnacevessel is provided with a preheating shaft, which is arranged above theelectric arc furnace vessel and via a gas-permeable, cooled shut-offdevice opens into the electric arc furnace vessel.

[0043] An alternative embodiment is characterized in that the preheatingshaft is arranged centrally above the electric arc furnace vessel andthe lid of the electric arc furnace vessel is designed to be annular soas to surround the preheating shaft and connect the same with side wallsof the electric arc furnace vessel, with electrodes, preferably graphiteelectrodes, projecting through the lid into the interior of the electricarc furnace vessel in an oblique manner.

[0044] Suitably, there are provided nozzles and/or lances and/or burnersopening into the interior of the electric arc furnace vessel andconnected either to a supply means for iron carriers and/or an oresupply means and/or a supply means for coal or carbon carriers and/or asupply means for slagformers and/or a supply means supplying oxygen oran oxygen-containing gas and/or a hydrocarbon supply means and/or asupply means for an inert gas.

[0045] Advantageously, nozzles and/or lances are arranged in theoxygen-blowing converter, which are connected either to a supply meansfor iron-carriers and/or an ore supply means and/or a supply means forcoal or carbon carriers and/or a supply means for slagformers and/or asupply means supplying oxygen or an oxygen-containing gas and/or ahydrocarbon supply means and/or a supply means for an inert gas.

[0046] Preferably, the nozzles are configured as sub-bath nozzles and/orbottom flushing bricks or the lances are arranged so as to be movable,in particular pivotable and/or displaceable in their longitudinaldirection.

[0047] According to a preferred embodiment, the electric arc furnacevessel is provided with (one) roughly centrally arranged electrode(s)projecting into the vessel from above as well as optionally with abottom electrode.

[0048] To enable a wide variety of uses of the plant, the preheatingshaft is preferably configured as a unit separable from the electric arcfurnace vessel and from the casing and exchangeable.

[0049] For easier handling, the lid of the electric arc furnace vesseland the lid of the oxygen-blowing converter vessel form a unit or areconfigured as a unit.

[0050] Suitably, there is provided at least one control and/or repairopening, preferably above the transition from the electric arc furnacevessel to the oxygen-blowing converter vessel.

[0051] To avoid major interruptions when individual plant parts are inneed of repair, an advantageous embodiment is characterized in that theoxygen-blowing converter vessel is constructed as a structural unitseparable from the electric arc furnace vessel and exchangeable.

[0052] Preferably, the electric arc furnace vessel is provided with abottom downwardly inclined in the direction towards the decanting vesseland merging into a roughly horizontally located bottom part of thedecanting vessel, with the lowermost point of the bottom being providedin the decanting vessel and a metal tapping means being provided at thelowermost point of the bottom of the decanting vessel.

[0053] A process for the production of metal melts, in particular steelmelts, such as crude steel melts is characterized by the combination ofthe following process steps:

[0054] in the electric arc furnace vessel, a pre-melt is produced andbrought to a predetermined temperature level and a predeterminedchemical composition,

[0055] the pre-melt flows into the oxygen-blowing converter vessel viathe overflow weir continuously and irreversibly,

[0056] the pre-melt is continuously refined in the oxygen-blowingconverter vessel, preferably to crude steel and

[0057] the refined melt is carried off the oxygen-blowing convertervessel continuously or discontinuously,

[0058] the slag forming in the oxygen-blowing converter vessel incounterflow flows into the electric arc furnace vessel, from which it iswithdrawn.

[0059] Suitably, prefining is carried out in the electric arc furnacevessel and final refining of the metal product in the oxygen-blowingconverter vessel.

[0060] Preferably, in the oxygen-blowing converter vessel a chemicalcomposition and a temperature of the metal melt are adjusted in acontinuous manner which correspond to the chemical composition andtemperature of the final melt or of the end product desired for tapping.

[0061] For adjusting a high melting efficiency, if is of advantage ifthe offgases formed in the oxygen-blowing converter vessel are withdrawnvia the electric arc furnace vessel, with CO+H₂-afterburning beingcarried out both in the oxygen-blowing converter vessel and in theelectric arc furnace vessel, wherein suitably the offgases arising inthe electric arc furnace vessel and the offgases flowing over into theelectric arc furnace vessel from the oxygen-blowing converter vessel areemployed for preheating the lumpy charge material charged into theelectric arc furnace vessel.

[0062] For better utilizing the energy, the offgases employed forpreheating are afterburned step-by-step during the preheating process.

[0063] Preferably, a negative pressure is maintained in the electric arcfurnace vessel and in the oxygen-blowing converter vessel.

[0064] An alternative advantageous process for the production of pigiron melts is characterized by the combination of the following processsteps:

[0065] to the electric arc furnace vessel, pig iron is charged in liquidform and is brought to a predetermined temperature level,

[0066] Si- and P-contents are lowered during prerefining in the electricarc furnace vessel,

[0067] the liquid pig iron flows continuously into the oxygen-blowingconverter vessel via the overflow weir,

[0068] the liquid pig iron is furthermore partially refined in acontinuous manner in the oxygen-blowing converter vessel as well,

[0069] the partially refined pig iron is drawn off the oxygen-blowingconverter vessel discontinuously or continuously and

[0070] the slag forming in the oxygen-blowing converter vessel flows incounterflow into the electric arc furnace vessel, from which it iswithdrawn, wherein the partially refined (pretreated) pig iron suitablyis finally refined to a liquid end product by conventional methods,without or with feeding of other iron carriers, in a converter orelectric arc furnace provided in addition to the plant.

[0071] Preferably, the metallic charge mix is formed from at least oneof the following components

[0072] scrap, such as steel scrap, and/or solid pig iron or cast iron,

[0073] direct reduced iron in the form of pellets and/or briquettesand/or iron carbide,

[0074] liquid pig iron.

[0075] For the production of alloyed steel melts or special steel meltsor stainless steel melts, the metallic charge mix is formed at leastfrom alloyed steel scrap and liquid and/or solid alloying agents and/orferroalloys.

[0076] Preferably, the steel melt tapped from the oxygen-blowingconverter vessel is subjected to further treatment as a pre-melt in asubsequent secondary metallurgical treatment including decarburization,either with or without negative pressure (vacuum). The vacuum treatmentcan be carried out in a VOD, RH-OB or KTB plant. The pre-melt alreadyexhibits a C content in excess of that demanded for the quality that isto be produced.

[0077] In case the C content after treatment in the oxygen-blowingconverter vessel is already as low as that desired for the final melt,the steel melt tapped from the oxygen-blowing converter vessel issubjected to further treatment as a final melt in a subsequent secondarymetallurgical treatment, f.i. in a ladle furnace or a flushing unit.

[0078] In order to avoid skulls due to the slag and to be able to carryout a quantity control in respect of the slag, a liquefying or reductiontreatment, respectively, of the slag is carried out in theoxygen-blowing converter vessel after predetermined process times.

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] In the following, the invention will be explained in more detailby way of several exemplary embodiments schematically illustrated in thedrawing, wherein

[0080]FIG. 1 is a vertical section through a plant of the inventionaccording to a first embodiment and

[0081]FIG. 2 represents a section along line II-II of FIG. 1.

[0082]FIGS. 3, 4, and 5, 6 as well as 7, 8 and 9, 10 each showalternative embodiments in illustrations analogous to FIGS. 1 and 2,respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] A furnace vessel 1 of a d.c. electric arc furnace is provided asan intermediate vessel between a decanting vessel 2 and a convertervessel 3 constructed as an oxygen-blowing converter, i.e., is directlyconnected with each of these vessels 2 and 3 so as to constitute acoherent reactor plant comprising three operating zones. The furnacevessel 1 of the electric arc furnace serves above all as a melting ormelt reduction and heating zone, the converter vessel 3 predominantly asa refining and heating zone and the decanting vessel 2 as a decantingzone (settling zone). At the side of the furnace vessel 1, a preheatingshaft 5 is placed on its lid 4, into which preheating shaft metalliccharging substances 7—primarily steel scrap, optionally also solid pigiron and/or sponge iron—may be charged, preferably by means of aconveying belt 8. Suitably, the conveying belt 8 is encased in a casing6, so that a heating part 9 is formed in which preheating of thecharging substances 7 can be effected by means of burners and/orafterburning nozzles 10 while they are being conveyed by the belt. Theheating part 9 and the preheating shaft 5 are directly connected witheach other. In the lid 4 of the furnace vessel 1 there is provided atleast one charging opening 11 for continuously feeding solid lumpy ironcarriers 12 (direct reduced iron, fine scrap, prereduced iron ore,sinter, scales, filter dust and/or sludge briquettes, optionally finescrap, etc.) and/or carbon carriers 13 (coal, coke, pressed parts oforganic light fraction etc.) and/or slag formers 14 (lime, fluorspar,quartz sand, bauxite, etc.). Feeding is via a conveying belt 15 orconveying belts. The unit comprised of the furnace vessel 1, theconverter vessel 3, the decanting vessel 2, the preheating shaft 5 andthe heating part 9 constitutes the core of a first embodiment of theplant according to the invention, which is represented in FIGS. 1, 2.

[0084] The furnace vessel 1 in the case of a d.c. configuration has asingle or in the case of an a.c. configuration has preferably severalgraphite electrodes 16 for supplying electric energy. The electrodes 16may, if necessary, be pivotable within an angle of inclination rangingfrom 0 to 30° relative to the vertical in the direction towards thecenter of the furnace vessel 1 and up to 10° in the opposite directiontowards the wall of the furnace vessel 1. The angle of inclination maybe differently adjusted and/or controlled for each individual electrode16 and during the melting operation this angle usually is about 15 to20°. Usually, the electrodes 16 are perpendicular and are not pivotable.A bottom anode provided centrally in the bottom 18 of the furnace vessel1 serves as a counter electrode 17 (if a direct current is employed).

[0085] The metallic charging substances 7 preheated in the preheatingshaft 5 by the rising hot offgases 19 pass into the furnace vessel 1 ofthe plant continuously, due to the continuous melting operationconducted at a continuous supply of electricity.

[0086] The charging into the furnace vessel 1 of solid iron carriers 12having oxidic iron portions (sponge iron, fine scrap, prereduced ore,dust briquettes, etc.) and, if necessary, of carbon carriers 13, such ascoke, pressed parts of organic light fraction, etc., and slag formers 14(lime, fluorspar, quartz sand, bauxite, etc.), is carried outcontinuously via charging openings 10 arranged in the lid 4, at avelocity adjusted to the discharge of the melt from the furnace vessel 1and from the converter vessel 3.

[0087] Liquid pig iron 20 is supplied into the furnace vessel 1continuously via a pig iron supply means 21 designed as a chute andopening into the furnace vessel 1. Via a slag door 22, which ispreferably provided on the side of the furnace vessel 1 located oppositethe chute 21 and through which slag may be removed as well, the processmay be controlled, an additional lance manipulator 23 may be introducedand maintenance work can be can be carried out in the region of thefurnace vessel 1.

[0088] As implied by the form of the plant, charging and melting withinthe furnace vessel 1 always takes place with a liquid sump 24. Thelatter renders feasible a nearly continuous quasi-stationary meltingoperation with foamed slag 25 and an electric arc 26 almost completelysurrounded by the same. This results in high transformer outputs andthermal efficiencies and low noise emissions.

[0089] To meet the following demands

[0090] processing of fine grained iron carriers 12′ (e.g., iron carbide,sponge iron screening rejects, filter dusts, etc.),

[0091] production and control of the foamed slag 25

[0092] acceleration of the melting procedure of the charging substances7, 12, 13, 14 by increased energy inputs into the electric arc furnace(including afterburning of CO and H₂ in the offgas 19 within or abovethe foamed slag 25) and balancing out concentration and temperaturegradients within the melt bath 24 as well as

[0093] replacement of a portion of the required electric energy bycheaper primary energies,

[0094] there are furthermore supplied to the furnace vessel 1

[0095] fine grained iron carriers 12′ and/or

[0096] fine grained coal 13′ or other carbon carriers (treated organiclight fraction, e.g., shredder light fraction) and/or

[0097] fine grained slag formers 14′ (lime, fluorspar, etc.) and/or

[0098] gaseous oxygen and/or other oxidizing gases 27 (CO₂, H₂O, etc.)as well as secondary air 28 (including O₂-enriched air) and/or

[0099] Cl or other hydrocarbons 29 and/or

[0100] inert gases 30 (N₂, Ar)

[0101] in controlled amounts adapted to local and time demands, via oneor several

[0102] protected and/or non-protected nozzles and/or lances 32 (movableand/or fixedly installed lances, optionally designed as combinedlances/burners 32 a) at various points within the lid and/or wallregions of the electric arc furnace above and/or below the surface ofthe slag for top-blowing or blowing in at least one of theabove-mentioned substances 12′, 13′, 14′, 27, 28, 29, 30 and/or

[0103] protected sub-bath nozzles 33 (preferably high-pressure nozzles)and/or bottom flushing bricks or sub-bath nozzles for blowing in atleast one of the above-mentioned substances 12′, 13′, 14′, 27 to 30, orflushing bricks for inert gases 30.

[0104] For reasons of clarity, not all of these devices have beenentered in FIG. 1.

[0105] A certain amount of liquid sump 24 having formed, the metal melt24 formed in the furnace vessel 1 runs over a weir 34 into the convertervessel 3 and there is refined and simultaneously heated till tapping.For this purpose, the converter vessel 3 comprises at least one,preferably several

[0106] nozzles, namely protected (protected by natural gas—Ar, CO₂ andhigher hydrocarbons being usable as protective gases as well) and/ornon-protected nozzles such as super-bath nozzles for afterburning and/orlances 35 (movable and/or fixedly installed lances, optionally designedas combined lances/burners) at various points in the lid and wallregions of the converter vessel 3 above and/or below the surface of theslag for top-blowing/blowing in at least one of the substances 12′, 13′,14′, 27 to 30 and/or

[0107] protected sub-bath nozzles 36 (and/or bottom flushing bricks forblowing in at least one of the substances 12′, 13′, 14′, 27 to 30 aswell as flushing bricks for inert gases 30, and/or

[0108] at least one opening 39 for the addition of lumpy iron carriers12, carbon carriers 13 and slag formers 14—individually or incombination

[0109] wherein, according to a preferred variant design of the convertervessel 3, the following is provided:

[0110] Through several lances 35 exclusively gaseous oxygen 27 istop-blown. The lances 35 are arranged roughly symmetrically in the lid37 of the converter vessel 3, are displaceable in the vertical directionand at the same time are pivotable within an angle of inclination ofabout 0 to 30° relative to the vertical in or against the flow direction38 of the metal melt 24.

[0111] Through several protected sub-bath nozzles 36 and/or flushingbricks arranged in the bottom of the converter 3 exclusively inert gas30 (N₂ and/or Ar at any desired mixing ratios) is fed. The sub-bathnozzles and/or flushing bricks 36 are provided in a roughly symmetricalarrangement in the bottom of the converter vessel 3.

[0112] Into the converter vessel 3 exclusively lumpy slag formers 14(lime, fluorspar, quartz sand, bauxite, etc.) are supplied exclusivelythrough the lid opening 39 by means of the conveying belt 40.

[0113] Roughly above the weir 34, a control and repair opening 50 isprovided.

[0114] The addition of the lumpy slag formers 14 through the lid opening39 in the converter vessel 3—approximately above a crude steel tapopening 41—accelerates the dissolution of lime and the formation of areactive refining slag 25 exhibiting high contents of iron oxide in theregion of the converter vessel 3.

[0115] Driven by its own gravity as well as by the impetus imparted bythe lances 35 and 35′, the refining slag 25 moves from the convertervessel 3 towards the furnace vessel 1 in counterflow to the metal melt24, in the direction of arrow 42, reaching metal melt 24 of constantlydecreasing temperature and increasing content of accompanying elements(C, Si, Mn, P, S, etc.), thus heating and refining the same and beingcooled and reduced by the same, until the slag 25 is tapped through aslag door 22 provided at the end of the decanting vessel 2.

[0116] The advantages of such a “metal/slag counterflow movement” are asfollows:

[0117] 1) Low heat and iron losses by the slag 25 when leaving thedecanting vessel 2 through the slag door 22, because, on the one hand,the slag 25 leaves the plant on the “cold side” and, on the other hand,so-called “Gaining out” of metal droplets from the slag 25 takes placein the decanting vessel 2 besides the iron oxide reduction occurringprimarily within the furnace vessel 1.

[0118] 2) Obtainment of the desired steel grade at a substantially lowerconsumption of slag formers 14 and a lower specific amount of the formedslag 25, respectively, and consequently at a lower refractory wear ofthe plant. Since the amount of slag in the converter vessel 3 depends onlevel of the metal bath, high retention times or very good utilizationratios of the slag can be achieved.

[0119] The hot offgases 19 formed within the converter vessel 3 at firstpass into the furnace vessel 1, mixing with the offgases forming there,before rising through the preheating shaft 5 and either (variant withoutheating part, FIGS. 5, 9) leaving the plant through an offgas duct 46provided in the upper region of the preheating shaft 5 or passing intothe heating part 9 (variant including a heating part, FIGS. 1, 2, 7, 8).Depending on the local heat demands in the various parts of the plant,the offgases on their way are partially afterburnt, preferably by oxygen27, optionally by air 28 or air/oxygen mixtures, via lances 32, 35and/or nozzles 47, nozzles 10 in the heating part. In doing so, highafterburning degrees are technically feasible at certain charging ratiosand under certain conditions of process control, amounting to above 50%if exiting the furnace vessel 1 and amounting to up to 90-100° C. ifexiting the preheating shaft 5 or the heating part 9. Thus, with theinstant process and plant concept by far the major portion of thechemical and sensible heat of the offgases 19 is transferred to themetal bath 24 either directly within the converter vessel 3 and thefurnace vessel 1 or indirectly by preheating the charging substances 7in the heating part 9 and/or preheating shaft 5, thus being immediatelyutilized for the process. At the same time, the probability ofuncontrollably high CO emissions is nearly eliminated. The charge in thepreheating shaft 5 acts as a filter and hence affords a reduction of thedust content in the offgas.

[0120] A lower consumption of electric energy as compared toconventional electric arc furnaces without scrap preheating (by about 25to 40%) and to discontinuously operated electric arc furnaces withintegrated scrap preheating (by about 15 to 25%) results for the plantand process concept according to the invention with identical chargingsubstances. Plant productivity is approximately doubled as compared to aconventional electric arc furnace without scrap preheating at anapproximately equal size and equipment of the electric arc furnace(transformer output, lances, burners, etc.).

[0121] Plant conception

[0122] The conception of the individual parts of the plant, such as

[0123] furnace vessel 1

[0124] preheating shaft 5

[0125] heating part 9 (if provided, preferred in the case of >30% scrapin the charge mix),

[0126] converter vessel 3,

[0127] decanting vessel 2

[0128] number and arrangement of the charging openings 11 in the furnacevessel 1 and 39 in

[0129] the converter vessel 3

[0130] is effected as a function of

[0131] the charging substances to be used, in particular iron carriers 7(shape, size, composition, temperature and state of aggregation)

[0132] the production output desired

[0133] the demands in respect of steel quality

[0134] the mode of operation desired for the plant (continuous orsemi-continuous—with discontinuous tapping), also in respect of thedesired integration with preceding and/or consecutively arranged plants(e.g., for pig iron production, direct reduction, secondarymetallurgical treatment, continuous casting, etc.)

[0135] the types and prices of the energy sources available.

[0136] The main goal in conception is to carry out the partial steps ofthe process, namely preheating, charging, melting or melt reduction,refining, heating and tapping within the plant at the same time, yetlocally offset and hence as independent of one another as possible, indifferent plant parts at a controllable course of operation underrespectively favorable physico-chemical, reaction-kinetic andheat-technological conditions, i.e., so to obtain an overall plantcomprised of nearly perfectly (highly effectively) working sectionalreactors for a concrete case of application.

[0137] The plant configuration according to the invention enables themutually independent emptying of the plant zone comprised of furnacevessel 1 and decanting vessel 2 on the one hand (via tap opening 43)and, on the other hand, of the converter vessel 3 via tap opening 41,without having to tilt the overall plant for that purpose, inspectionand minor repair work in the hot state of any of these two zones thusbeing feasible, if the necessity arises, at short notice whilethrottling the plant. According to the invention it is preferred thatall of the plant parts be firmly interlocked as a unit and immovable oruntiltable during operation. Due to the preferred sectionalconfiguration of both the lower vessel and the lid 4 and 37 of theplant, individual or several parts or vessels in need of repair can beexchanged upon lateral retraction (which also applies to the preheatingshaft 5). To avoid prolonged interruptions of production, the exchangevessel concept is preferred, i.e., ready-to-use, optionally preheatablestand-by vessels (f.i. a converter vessel 3 and a unit comprised of afurnace vessel 1 and a decanting vessel 2) are available within a shorttime. Plant variants depending on the charge mix (guidelines forselecting the overall plant configuration):

[0138] An overall plant configuration with scrap preheating shaft 5 andheating part 9, as represented in FIG. 1, is applicable in cases where aspecific minimum portion of solid scrap 7 within the charge mix isemployed. As a general guideline for selecting the overall plantconfiguration as a function of the charge mix, the following Table I canbe used: TABLE I Portion of scrap (%) Plant configuration in the chargemix as a Variant, selection criterion Main plant parts represented inFIG. <15% furnace vessel 1, converter 3/4 vessel 3 15-30% preheatingshaft 5, furnace 5/6, 9/10 vessel 1, converter vessel 3 >30% heatingpart 9, preheating 1/2, 7/8 shaft 5, furnace vessel 1, converter vessel3

[0139] According to FIGS. 3, 4, the scrap portion 12 is introduced intothe furnace vessel 1 and/or into the converter vessel 3 via the lidopenings 11 or 39 by means of the conveyor-belt-and chute system 15, 15′or 40, with the maximum dimension of the scrap pieces 12 not beingallowed to exceed a predetermined measure (f.i. 200 mm).

[0140] According to FIGS. 5, 6, the scrap preheating shaft 5 has only asmall cross-section since only a small quantity of scrap is charged, andit is charged continuously by means of a scrap conveying belt 8 withouta preheating function, i.e. without a heating part 9. With this variant,oversize scrap pieces must, if necessary be separated and cut prior tocharging. Carrying-off of the offgases is in the upper, so-called hoodregion 5′ of the scrap preheating shaft 5 via the offgas duct 46.

[0141] In accordance with the variants illustrated in FIGS. 1, 2 and 7,8, at least one scrap preheating shaft 5 is continuously charged bymeans of at least one scrap conveying belt 8 with preheating function,i.e. by means of a heating part 9. Depending on

[0142] the charge mix (in particular the scrap portion)

[0143] the actual space and height conditions existing in a given caseof application (the plant layout)

[0144] the desired operating parameters (plant productivity, consumptionof electric energy, availability of fossil fuels, such as f.i. naturalgas, coal, etc.), f.i. the following variants of embodiments of scrappreheating shaft 5 and heating part 9 are conceivable here:

[0145] a scrap preheating shaft 5 with a heating part 9 with one scrapconveying belt 8 or several scrap conveying belts 8 arranged in parallelrelationship (FIGS. 1, 2)

[0146] two scrap preheating shafts 5 (FIGS. 7, 8) having one heatingpart 9 each or sharing a common heating part 9, with each heating part 9encasing at least one scrap conveying belt 8

[0147] Carrying-off of the offgases 19 is via a hot gas duct (notillustrated) disposed at the beginning of the heating part 9.

[0148] According to the variant shown in FIGS. 9 and 10, a preheatingshaft 5 with a gas-permeable and water-cooled shut-off device 5″ ismounted on top of the lid 4 of the furnace vessel 1, which shaft can becharged with metallic charging substances 7—predominantly steel scrap,optionally even solid pig iron—preferably via a conveyor belt 15. Thefurnace vessel 1 is equipped with several catholically switched obliquegraphite electrodes 16, which are optionally configured as hollowelectrodes and are preferably disposed in a symmetrical arrangementrelative to the electric arc furnace and the mounted preheating shaft 5.The electrodes 16 are pivotable within an angle of inclination of 0 to30° relative to the vertical in the direction of the center of thefurnace vessel 1 and up to 10° in the opposite direction towards thewall of the furnace vessel 1. The angle of inclination may be adjustedand/or controlled differently for each individual electrode 16. Duringthe melting operation it usually amounts to about 15 to 20°.Occasionally, pivotability of the electrodes 16 may be renounced. Ascounter electrode 17 there serves a bottom anode arranged centrally inthe bottom 18 of the furnace vessel 1.

[0149] The fundamental principles of the functioning and control of theprocess may be summed up as follows:

[0150] Supply of the charging substances/process media and discharge ofthe products:

[0151] Continuous supply of the charging substances and media atcontrollable velocity into the furnace vessel 1 (principal amount) andsimultaneously into the converter vessel 3 (a partial amount thereof asa cooling agent).

[0152] Continuous discharge of the products from at least two plantparts, namely preferably crude steel from the converter vessel 3 andslag 25 from the decanting vessel 2 arranged directly adjacent thefurnace vessel 1 as well as offgas 19 depending on the plantconfiguration in accordance with the charge mix:

[0153] from the furnace vessel with the plant variant of FIGS. 3, 4,

[0154] from the preheating shaft 5 with the plant variant of FIGS. 5, 6and the variant of FIGS. 9, 10 or

[0155] from the heating part 9 with the plant variant of FIGS. 1, 2 aswell as of FIGS. 7, 8

[0156] It is feasible to discontinuously tap crude steel from theconverter vessel 3 with or without a throttling of the overall plant,wherein, if requirements regarding the quality of the crude steel arehigh, a retaining dam is mounted on the overflow weir 34 on the furnaceend thereof, to limit or prevent backflow of the furnace slag 25 intothe converter vessel 3 during discontinuous tapping of crude steel andthereafter (until establishment of equal slag levels within the furnacevessel 1 and within the converter vessel 3).

[0157] Process sequence and mixing ratios:

[0158] in the case of continuous crude steel tapping—continuoussemi-stationary condition with respect to the temperature,concentration, flow, mixing and quantities of the metal, slag and offgasin each vessel of the overall plant

[0159] in the case of discontinuous crude steel tapping—with apronounced tapping cycle in regard of the above-listed criteria withregard to metal and slag in the converter vessel 3 and with regard toslag in the furnace vessel 1, otherwise semi-stationary

[0160] Irrespective of the manner of tapping the crude steel(continuously or discontinuously), the following requirements concerningthe process course are fulfilled continuously:

[0161] intensive mixing of the bath within the furnace vessel 1 andwithin the converter vessel 3,

[0162] large reaction and heat-exchanging surfaces in all plant parts,

[0163] crude steel in the converter vessel 3 is at all times maintainedat the composition and temperature desired for tapping.

[0164] Preheating, melting, refining and temperature control:

[0165] A stepwise change of the physico-chemical properties of thecharging substances is effected (in particular of the temperature, thechemical composition and the condition of matter) with a view toproducing crude steel melt as the main product as well as slag andoffgas as by-products with optimum utilization of energy in accordancewith the following scheme:

[0166] In the heating part 9 and preheating shaft 5:

[0167] Preheating of the scrap (up to 100% of the scrap in the chargemix) taking into account the criteria for selecting the plantconfiguration, wherein in the heating part 9 (if provided) preheating toa low temperature, f.i. max. 400-450° C., is effected and in thepreheating shaft 5 (if provided) preheating to a more elevatedtemperature, f.i.≦800° C. (scrap preheating temperatures of 1000° C. andhigher are perfectly feasible, possibly with a lined preheating shaft)is carried out.

[0168] It is also feasible to preheat other charging materials besidescrap, such as f.i.

[0169] lumpy slag formers (dolomite, quartzite etc.),

[0170] lump coal or lump coke,

[0171] optionally sponge iron (up to a limited portion of the chargingsubstances by means of the heating part 9 and/or the preheating shaft5),

[0172] yet, taking into consideration possible undesirable phenomena(re-oxidation, increased flame chipping, etc.), in dependence on theirretention time and the preheating temperature in the heating part 9and/or preheating shaft 5.

[0173] In the furnace vessel 1:

[0174] melting of the major portion (principal amount) of the chargingsubstances in the charge mix (except for the smaller partial amount ofthe charging substances provided as cooling agents, which are needed inthe converter vessel 3 and are directly charged there) and at the sametime

[0175] carburization and prefining of the metal with the aim ofproducing a pre-melt having approximately the following properties independence of the charge mix:

[0176] % Si≦0.10

[0177] % C=1.0-3.0

[0178] T=1540-1560° C. (Ø about 1550° C.),

[0179]  which pre-melt flows aver into the converter vessel 3, with themean decarburization velocity amounting to 0.06 to 0.10 (max. 0.12) %C/min in dependence on the charge mix, and

[0180] under continuous feeding of cold charge-mix components, e.g.sponge iron and/or iron carbide, optionally fine scrap and/or hotcharge-mix components, e.g. liquid pig iron (from a precedingly arrangedblast furnace or a melt reduction), hot sponge iron and/or iron carbideand lump coal and/or fine coal (coke, SLF), lumpy and/or dust-like slagformers (lime, dolomite, quartzite, fluorspar, etc.).

[0181] In the converter vessel 3:

[0182] continuous final refining (mainly decarburization as well asin-depth dephosphorization) and at the same time heating of the high-Cpre-melt constantly overflowing from the furnace vessel 1 to the crudesteel composition and temperature which are desired for the tapping ofthe crude steel and are already (at all times) adjusted in the convertervessel, while balancing out the concentration and temperature byintensive mixing of the bath (homogenization) at

[0183] continuous feeding of lumpy and/or fine-grained cooling agents(incl. charge-mix components) and/or slagformers, and/or carboncarriers, f.i. sponge iron and/or iron carbide, fine scrap, ore, scales,metallurgical dusts/sludges, limestone, dolomite, lime, quartzite,fluorspar, etc., coal, (coke), treated shredder light fraction and

[0184] without interrupting the refining process during a discontinuoustapping of crude steel, if provided, i.e. without interrupting andconsiderably influencing the process course in the precedingly connectedplant parts (optionally slight throttling may be feasible),

[0185] with the preferred decarburization velocity amounting to 0.08 to0.13 (max. 0.15) % C/min in dependence on the charge mix.

[0186] Slag control

[0187] The concept of the process is based on a countercurrent movementof metal 24 and slag 25 in the region furnace vessel 1/converter 3, i.e.the slag moves from the converter vessel 3, which is the plant part withthe highest temperature and the highest oxygen potential of the metalbath, via the furnace vessel 1—this latter has a lower temperature and alower oxygen potential of the metal bath, since it contains a metal meltrich in C—in the direction of the slag door 22 at the end of thedecanting part 2, where the slag 25 may first leave the plant. Thedriving force behind this movement of the slag 25 is, above all,gravity, assisted by impulses transmitted to the slag 25 due to theintensive mixing of the bath in the converter vessel 3 and in thefurnace vessel 1. In the course of this movement (especially whentraversing the furnace vessel 1), the slag 25 encounters a metal melt 24having a low temperature and higher contents of Si and C and, due to theintensive mixing of the bath, is reduced with respect to FeO content bythat melt and at the same time is cooled by it. In addition to this, thepartial amount of the slag 25 from the converter vessel 3 mixes withnonmetallic phases arising in the furnace vessel 1 and in the decantingpart 2, namely

[0188] from the gangue and ashes of the components of the charge mix(sponge iron, HBI, iron carbide, scrap, etc.),

[0189] from the oxidation of Si, Mn, P and other elements with anaffinity for oxygen which are present in the charge mix (liquid and/orsolid pig iron, scrap etc.),

[0190] from the slagformers supplied to the furnace vessel 1, which areadded f.i. as correction fluxes,

[0191] from the refractory wear in the furnace vessel 1 and in thedecanting part 2, as a result of which the amount of the formed slag 25in the furnace vessel 1 considerably larger than that of the slag formedin the converter vessel 3. After a certain “quieting” of the slag 25 inthe decanting part 2 (without intensive mixing of the bath) and partialraining out of the metal droplets it contains, the slag 25 leaves theplant through the slag door 22 at the end of the decanting part 2.

[0192] In contrast to the discontinuous process, an important processfeature is to be seen in that the specific amount of slag, based on theamount of metal in the converter vessel 3, is not equal to the verysmall amount of slag per ton of the pre-melt overflowing from thefurnace vessel 1 but is much higher, and when operating in thecontinuous crude steel tapping mode and with a nearly constant level ofthe metal melt in the converter vessel 3 it is determined by the heightdifference between the furnace vessel 1 and the converter vessel 3 ormay be controlled thereby within certain boundaries. At the same time,this process feature has the effect that the retention time in theconverter vessel 3 of the slag 25 (with very good properties concerningdephosphorization and desulphurization) formed within the convertervessel 3 is considerably higher than f.i. in a discontinuous LDconverter and, besides, can be controlled, whereby the followingadvantages result:

[0193] improved utilization of the refining properties of theslagformers supplied to the converter vessel 3,

[0194] the possibility of achieving very low contents of P and S in thecrude steel (one contributive factor in this respect is the process andplant configuration, which in principle corresponds to a discontinuousprocess with intermediate tapping of a partial amount of the slag),

[0195] no danger of formation of skulls in the oxygen-blowing lance 35in the converter vessel 3 due to a very small amount of slag, which iswell known to occur f.i. with discontinuous converter processes withcharging of pretreated pig iron (deSi+deP) and slag-poor refining (slagminimum process) at ≦30 kg slag/t steel.

[0196] To better utilize the slagformers supplied in the furnace vessel1 it is of advantage to introduce them in the form of lumps that are assmall as possible, so that their dissolution in the slag 25 will be asrapid and complete as possible. This applies especially to lime anddolomite. By preferably feeding up to 100% of the lime or the dolomiteto the furnace vessel 1 in fine-grained condition (as powdered lime orpowdered dolomite, respectively), it is also feasible to considerablylimit the negative effects of the so-called “hot spots” in the case ofthe furnace being configured as an a.c. To the converter vessel 3, lumpyslagformers are preferably supplied (fine-grained slagformers being fedonly in the case that extreme requirements with regard to the quality ofthe crude steel must be met with).

[0197] The properties of the slag 25 in the converter vessel 3 and inthe furnace vessel 1 (roughly identical with the final slag at exit fromthe slag door 22 on the end of the decanting part 2) as they arepreferred according to the invention may be summed up as follows:

[0198] Converter slag

[0199] in the range of technical lime saturation

[0200] % CaO/% SiO₂≧3.4

[0201] % MgO≧7

[0202] % FeO_(n)=25-30 in the case of crude steel

[0203] % C=0.03-0.05

[0204] T_(tap)=1620-1630° C.

[0205] preferred feeding of lumpy slagformers (lime, dolomite,quartzite)

[0206] preferred retention time in the converter vessel 3: ≧80 min

[0207] furnace slag=final slag at emergence from the plant

[0208] % CaO/% SiO₂=1.8-2.0

[0209] % MgO≧7

[0210] % FeO_(n)=10-15% in the case of pre-melt

[0211] % C=1.0-3.0

[0212] T_(overflow)=1540-1560° C.

[0213] EAF→LD

[0214] preferred feeding of fine-grained slagformers (in particularpowdered lime, powdered dolomite) via several nozzles/lances in/throughthe furnace lid 4, supply of materials into the “hot-spot” areas

[0215] These basic principles of slag control also apply to the processvariant with discontinuous tapping of crude steel. No essentialdifference arises due to the dam which optionally is to be used here andwhich is only employed in the case of high quality requirements.

[0216] Offgas parameters (capturing, afterburning, temperature, dust andpoisonous components in the crude gas):

[0217] Offgas from the converter vessel 3 and from the furnace vessel 1is concertedly withdrawn through the scrap preheating shaft 5, whereprovided, and optionally through the heating part 9, wherein thechemical and the physical heat of the offgas are optimally (distributedand) utilized; if no preheating shaft 5 is provided, the offgases fromthe furnace vessel 1 pass into the hot gas duct directly connectedthereto. Nearly 100% of the offgas are captured by a shut-off systemwith a minimum of uncontrolled emissions and a minimal load due to heat,dust and poisonous components in the offgas, as there is no need foropening a plant part for carrying out charging operations. The offgasesare afterburned to an increasing extent as they proceed from theconverter vessel 3 to the furnace vessel 1 and onward to the preheatingshaft 5 as well as to the heating part 9, depending on the givenrequirements and the charge mix. Note the folowing standard values: CO +H₂-degree of offgas temperature Plant part afterburning % ° C. convertervessel 3 10-15 T≦1700 furnace vessel 1 about 30 without shaft T≦1700about 40 with shaft preheating shaft 5 60-70 800≦T≦1500 heating part 4 85-100 800≦T≦1300 Preferred media for offgas afterburning Type of mediaPreferred application O₂ converter vessel 3 O₂ + air furnace vessel 1,preheating shaft 5 air heating part 9

[0218] For all plant parts, O₂/air mixtures are available whose mixingratios can be adjusted as desired.

[0219] Additional heat sources/energy supply for satisfying the heatdemand

[0220] Standard values according to the following table: Standardportion for meeting the heat demand, (%) Oxidation of accompanying PlantOxidation elements C, Si CO + H₂ Electric part of Fe etc.¹ afterburningBurner energy heating 3-9 <1 ≧80  0-10 — part 9 preheating 20-30 <1 ≧70— — shaft 5 furnace — 10-20 15-20 10-15 50-60 vessel 1 converter 15-25≧60 10-15 — — vessel 3

EXAMPLARY EMBODIMENTS

[0221] The three following exemplary embodiments illustrate thetechnological sequence and the results achievable in the application ofthe process and plant variants of the invention for continuouslyproducing crude steel from the charging substances (iron carriers) thatare most important worldwide, such as steel scrap, sponge iron andliquid pig iron. The charge mix is different for each exemplaryembodiment, namely:

Exemplary Embodiment 1

[0222] 100% steel scrap

Exemplary Embodiment 2

[0223] 40% steel scrap

[0224] 30% sponge iron

[0225] 30% liquid pig iron

Exemplary Embodiment 3

[0226] 50% sponge iron

[0227] 50% liquid pig iron

[0228] The process and plant variants of the invention also allow thecontinuous production of crude steel from 100% sponge iron or from 100%liquid pig iron, wherein in the latter case ore, carbonate, scales, dustbriquettes, etc. may be employed as cooling agents individually or incombination.

[0229] In addition to the Fe-containing charging substances, there arealso used in accordance with the Exemplary embodiments:

[0230] fluxes: soft burnt lime, dolomite, quartzite

[0231] gases: oxygen, nitrogen, natural gas, air (compressor andventilator)

[0232] solid coal: lump coal, fine coal (blowing coal)

[0233] refractory materials: bricks for lining the furnace—and also theconverter vessel 3, gunning materials (repair)

[0234] graphite electrodes: for the furnace vessel 1 and

[0235] cooling water: for water cooled panels of the furnace vessel 1,of the preheating shaft 5 and of the heating part 9

[0236] all of which are customary in steel-making practice. In spite ofbeing more cost-advantageous and/or being of advantage in view of abetter steel quality, the possible use of alternative

[0237] Fe-containing charging substances: solid pig iron

[0238] as Fe-carriers and/or as cooling agents: iron carbide, filterdust, scales, dried sludge, ore (Fe—/Mn ore)

[0239] fluxes: fine lime, fine dolomite, fluorspar

[0240] media: Ar (for inert-gas bottom flushing)

[0241] energy sources: shredder light fraction

[0242] is renounced in the following exemplary embodiments.

[0243] The quality and the temperature of the available chargingsubstances and gases can be seen from Tables II, III and IV.

[0244] For carrying out the process, the following plant configurationsare employed:

Exemplary Embodiments 1 and 2

[0245] Plant according to FIG. 1 comprising

[0246] a heating part 9 (conveyor belt 8 with preheating function)

[0247] a scrap preheating shaft 5 of oval cross-section

[0248] a furnace vessel 1 configured as an AC-EAF as a melting andprefining vessel

[0249] a converter vessel 3 of the type LD-S*

[0250] a decanting part 2 associated with the furnace vessel 1

Exemplary Embodiment 3

[0251] Plant according to FIG. 3, comprising

[0252] an AC electric arc furnace as the furnace vessel 1, as themelting and prefining vessel

[0253] a converter vessel 3 of the type LD-S*

[0254] a decanting part 2 TABLE II Chemical composition and temperatureof the Fe-containing charging substances steel scrap 0.30% C 2.5% ashes0.50% Mn 0.2% moisture 0.20% Si 0.030% S 25° C. 0.020% P sponge ironpellets 91.9% FE_(tot) (MIDREX-DRI) 92.9% degree of metallization 1.8% C4.6% gangue about 0.5 gangue basicity 25° C. liquid pig iron 4.2% C1320° C. 0.5% Mn 0.6% Si 0.04% S 0.09% P

[0255] TABLE III Chemical composition, grain size and temperature offluxes, solid fuels and refractory materials lime (10-30 mm) dolomite(10-30 mm) quartzite (<5 mm) 92.0% CaO 54.0% CaO 96.0% SiO₂ 1.0% MgO41.0% MgO 2.4% SiO₂ 2.9% SiO₂ 25° C. 25° C. 25° C. lump coal fine coallining (bricks) (3-15 mm) (<3 mm) EAF and LD converter 84.0% C 92.0% C96.5% MgO 97.0% MgO 0.5% S 0.5% S  2.1% CaO  1.9% CaO 9.4% volatilematter 2.0% volatile matter 6.1% ashes 5.5% ashes 10% C* 10% C* 25° C.25° C. 1550° C. 1620° C. gunning materials: ≧95% MgO

[0256] TABLE IV Chemical composition (vol. %), temperature of gasesnitrogen natural oxygen oxygen (conveyance + air (ventilator air, gas(lances) (burner) flushing) compressor air) 96 v. % 99.7 v. % 96.0 v. %99.9% N₂ 79 v. % N₂ CH₄ O₂ O₂ 21 v. % O₂ 25° C. 25° C. 25° C. 25° C. 25°C.

[0257] In all three embodiments, the furnace vessel 1 and the convertervessel 3 exhibit the following, identical configuration and equipment,with the specification referring to conventional discontinuous plantsaccording to standard lines:

[0258] Specification of the furnace vessel 1:

[0259] a vessel diameter of about 6 m corresponds to a discontinuous tapweight of 90 t crude steel at about 11 t liquid sump (residual sump),

[0260] 70 MVA transformer output, a.c.,

[0261] three pieces of graphite electrodes 16, each 560 mm in diameter(no bottom anode 17, due to a.c. power supply),

[0262] one pig iron chute 21 for continuously supplying liquid pig iron20,

[0263] two charging openings 11 arranged in the lid 4 for continuouslysupplying sponge iron pellets and/or fine scrap 12, lump coal 13 andlumpy slagformers (lime, dolomite, quartzite) 14 transported to the spotvia a conveyor-belt-and-chute system 15,

[0264] three pieces of lime nozzles in the lid 4 of the furnace vessel 1for continuously blowing in up to 100% of the amount of lime anddolomite supplied in the furnace vessel 1 as lime dust or powdereddolomite 14 into the hot spots using air 28 as a carrier gas,

[0265] two pieces of water-cooled manipulator lances (one lance 32through the sidewall of the furnace vessel 1, one lance 23 through theslag door 22 in the decanting part 2 projecting on into the furnacevessel 1) for continuously blowing in gaseous oxygen 27 and/or fine coal13 (air 28 as a carrier gas) below the surface of the slag 25 within thefurnace vessel 1,

[0266] three pieces of coal sub-bath nozzles 33 for continuously blowingin fine coal 13 using air 28 as a carrier gas,

[0267] six pieces of inert-gas sub-bath nozzles 33 for continuouslyblowing in an inert gas 30 (N₂/Ar, ratio adjustable as desired) forintensive intermixing of metal 24 and slag 25 in the furnace vessel 1,

[0268] three pieces of O₂ sub-bath nozzles 33 for continuously blowingin gaseous oxygen 27, with the O₂ sub-bath nozzles 33 being protectedwith natural gas or LPG (liquid propane gas) 29 and disposed in thebottom of the furnace vessel 1 preferably below the scrap preheatingshaft 5,

[0269] five pieces of natural gas/oxygen burners 32 a with a capacityper burner of max. 3.5 MW, disposed in the side wall of the furnacevessel 1 in a roughly symmetrical arrangement below the scrap preheatingshaft 5,

[0270] three pieces of afterburning nozzles 35 in the lid 4 of thefurnace vessel 1 for gaseous oxygen 27 and/or air 28 (O₂/air ratioadjustable as desired), which are preferably configured as movable shortlances, i.e. as afterburning lances,

[0271] a lid 4 of the furnace vessel 1, which lid on its outside isformed from water-cooled panels which are provided with a refractorylayer from the inside (furnace interior),

[0272] a wide part of the side wall of the furnace vessel 1 on the sideof the converter vessel 3, which part is constructed as a weir 34,resulting on the one hand in a division of the lower part of the plantinto a furnace vessel 1 and a converter vessel 3, and on the other handin the formation of an upper part which is common to the two vessels,such that a continuous transfer of metal melt 24, slag 25 and offgas 19between the reactor parts 1 and 3 is accomplished by means of gravityalone, with metal 24 flowing in a direction opposite to that of the slag25 (so-called metal/slag counterflow movement), the offgases from thesubdivisions within the furnace vessel 1 and the converter vessel 3being driven through the charged scrap 7 inside the furnace vessel 1 andin the scrap preheating shaft 5 located directly thereabove by means ofthe concerted offgas suction, or, as illustrated in FIG. 3, passdirectly from the furnace vessel 1 into the hot gas duct of the offgastreatment plant (not illustrated), in case the overall plantconfiguration does not provide for a scrap preheating shaft 5 and/orheating part 9.

[0273] Specification of the converter vessel 3:

[0274] internal volume after fresh lining about 76.5 m³,

[0275] specific volume about 0.85 m³/t metal content corresponds roughlyto a discontinuous tap weight of about 90 t/crude steel for aconventional plant),

[0276] one water-cooled converter lance (top lance) for top-blowing max.10000 Nm³ O₂/hour,

[0277] three pieces of afterburning nozzles 35 for gaseous oxygen 27and/or air 28 (O₂/air ratio adjustable as desired) in the lid 37 and inthe upper conical part of the converter vessel 3, which are preferablyconfigured as movable short lances, i.e. as afterburning lances,

[0278] two charging openings 39, of these preferably only one inoperation (only one of them is illustrated in FIGS. 1 and 3) in theconverter lid 37 for continuously supplying fine scrap (here: shredderscrap of ≦100 mm piece size) and/or sponge-iron pellets (DRI) 12, lumpcoal 13 and lumpy slagformers (lime, dolomite, quartzite) 14, which aretransported to the spot via a conveyor belt/chute system 40,

[0279] six pieces of inert-gas sub-bath nozzles 36 for continuouslyblowing in an inert gas 30 (N₂/Ar, ratio adjustable as desired) forintensive intermixing of metal 24 and slag 25 in the converter vessel 3,

[0280] a crude steel tap opening 41 with a control unit for the tappingvelocity of the crude steel 24 as well as automatic closing means (notexplained more fully here) for interrupting the otherwise-continuoustapping operation, if necessary,

[0281] a lid 37 of the converter vessel 3, which lid is of aconstruction identical to that of the lid 4 of the furnace vessel 1 and,in interlocked condition, forms a unit (sectional configuration)therewith during operation. Roughly above the weir 34, it is providedwith a control and repair opening 50. That opening remains closed duringthe continuous process course.

[0282] Specification of the scrap preheating shaft 5, the heating part 9and the scrap-conveying belt 8:

[0283] To fulfil the rather diverse requirements regarding the supplyand preheating of scrap with the three embodiments under consideration(100%, 40%, 0% scrap in the charge mix), the following means areprovided:

[0284] 1. A scrap preheating shaft 5 having a large internal effectivecross-section of about 11.5 m² and rounded edges, as illustrated inFIGS. 1 and 2.

[0285] a roughly constant shaft cross-section throughout the shaftheight,

[0286] the shaft height above the lid 4 of the furnace vessel 1, i.e.above the level of entry of the shaft into the furnace vessel 1 up tothe upper hood region (lid) of the preheating shaft 5 is about 6.50 m,wherein

[0287] the preheating shaft 5 is formed from water-cooled panels whichin the upper hood region are internally provided with refractory plates(as can be seen in FIG. 1),

[0288] the preheating shaft 5 is provided with twelve afterburningnozzles 47 for oxygen 27, air 28 or an oxygen/air mixture, with theseafterburning nozzles 47 being disposed in a roughly symmetricalarrangement on the outer perimeter of the shaft in two planes, with sixnozzles being provided in each plane,

[0289] in the upper hood region of the preheating shaft 5 there areprovided two natural-gas/oxygen/air combined burners 10 which at thesame time may also be used as afterburning lances and as burners may beoperated with max. 3.5 MW per burner.

[0290] Basically, the entire preheating shaft 5 may be constructed fromwater-cooled panels with an internal brick lining, whereby the followingadvantages may be achieved:

[0291] low heat losses by the cooling water in the preheating shaft,i.e. a smaller quantity of cooling water is needed

[0292] higher scrap preheating and offgas temperatures at exit from theshaft are adjustable without the danger of breakdown

[0293] 2. A scrap preheating shaft 5 having a small internal effectivecross-section of about 5 m² and rounded edges (as illustrated in FIG.1):

[0294] a roughly constant shaft cross-section throughout the shaftheight,

[0295] total shaft height about 6.50 m, wherein

[0296] the preheating shaft 5 consists of water-cooled panels whichinternally are provided with refractory plates in the upper hood region,

[0297] the preheating shaft 5 is provided with eight afterburningnozzles 47 for oxygen 27, air 28 or oxygen/air mixtures, with theseafterburning nozzles 47 being disposed in a roughly symmetricalarrangement on the outer perimeter of the shaft in two planes, fournozzles being arranged in each plane,

[0298] in the upper hood region of the shaft 5 there is arranged anatural gas/oxygen/air combined burner 10 which at the same time mayalso be used as an afterburning lance and in its capacity as a burner isdesigned for a capacity of max. 3.5 MW.

[0299] 3. A heating part 9 is provided with two identical scrapconveying belts 8 disposed in parallel side by side inside the heatingpart 9, which belts are spatially isolated from each other within thecommon casing by a refractory dam (not illustrated in the drawings). Theconception of the heating part 9 and the scrap conveying belts 8 can besummed up as follows: Scrap conveying belt 8 number (identicalconstruction): 2 belt width: 2.0 m belt length: 40.2 m mean belt loading(t scrap/m² belt surface): 0.30 t/m² belt velocity: max. 8 m/min scrapconveying capacity per belt 8: max. 4.8 t/min Heating part 9 shape ofthe casing top: shaped like a partial circle, water-cooled panels withbricklining on their inner face bottom: rectangular, water-cooledpanels, without bricklining

[0300] Ten natural-gas/oxygen/air combined burners/lances 10 (ifoperated as burners: max. 3.5 MW per burner, or if operated asafterburning lances: max. 3000 Nm³/h air or air/O₂ mixture per lance10), disposed in two rows (five pieces in each row) in the brick lid ofthe heating part 9 in a symmetrical arrangement above each of the twoscrap conveying belts 8.

[0301] A vertically oriented refractory dam (wall) dividing the entireinterior space of the heating part 9 in the longitudinal direction intotwo subdivisions almost completely separate from each other, having onescrap conveying belt 8 each.

[0302] Course of process and results

Exemplary Embodiment 1

[0303] The charge mix consists of 100% steel scrap (mixed scrap) havingthe composition shown in Table II. The process is carried out using theplant variant according to FIG. 1 with the scrap preheating shaft 5having an internal effective cross-section of 11.5 m² and with two scrapconveying belts 8 (each with a belt width of 2.0 m and a belt length of40 m), which are arranged in parallel side by side and prior tounloading the scrap 7 into the preheating shaft 5 pass through a commonheating part 9 which is 10 m in length, with the heating part 9 openingdirectly into the upper hood region of the preheating shaft 5.

[0304] A small partial amount (1.50%) of the scrap with a piece size≦100 mm is fed into the converter vessel 3 continuously as a coolingagent 12 at a temperature of 25° C. The rest of the scrap, which has amax. length of the scrap pieces of 1.5 m (i.e. the principal partialamount 7 of 88.50%), is charged onto the two scrap conveying belts 8 bymeans of four scrap charging cranes and after preheating in the heatingpart 9 and in the preheating shaft 5 is fed to the furnace vessel 1 in acontinuous manner and is melted therein. The mean height of the scrapcolumn 7 in the preheating shaft 5 is about 2.5 m. The heat sourcesemployed for preheating the scrap 7 in the heating part 9 and in thepreheating shaft 5 are the sensible heat (enthalpy) and the chemicalheat (heat from the partial afterburning) of the offgases 19 flowinginto the preheating shaft 5 or into the heating part 9 predominantlyfrom the furnace vessel 1 as well as the heat arising from a certainscrap oxidation taking place during the preheating of the scrap. Thepartial afterburning of the offgases 19 in the preheating shaft 5 iscarried out in two steps, with cold air 28 and gaseous oxygen 27 beingblown in continuously through the twelve afterburning nozzles 47disposed in two planes, in a ratio of volumes of roughly air/O₂˜4.2. Inthe heating part 9, afterburning is effected in a step-wise manner alongthe heating part 9 by continuously blowing in cold air 28 through the—inall—ten combined burners/lances 10 (here only as afterburning lances)arranged in the lid of the heating part 9 (2×5 combined burners/lances10 above each scrap conveying belt 8).

[0305] Important process variables for the process course in the heatingpart 9 and in the preheating shaft 5 are given in the following table:Process variable (input)output Unit Heating part 9 Preheating shaft 5 1.Scrap parameters flow rate* t/min about 4.6 about 4.6 amount t about11.9 about 21.3 retention min about 2.6 about 4.7 time temperature ° C. 25/327  327/834 oxidation % 0.31 1.70 2. Offgas parameters flow rateNm³/min  672/1111 522**/672 temperature ° C. 829/812 1571**/829 degreeof % 66.0/97.6 38.5**/66.0 afterburning (total CO—H₂) dust content g/Nm³about 49.0 about 76.4 3. Metallic % 99.8 101.2 yield***

[0306] Continuous melting of the scrap 7 preheated in the heating part 9and in the preheating shaft 5 is carried out in the furnace vessel 1,with the thus-forming metal melt 24 being at the same time carburizedand partially refined to a melt poor in Si but rich in C and having theproperties 1.86% C about 1550° C. 0.20% Mn ≦0.05% Si liquidustemperature about 1400° C. 0.032% S 0.005% P

[0307] in the furnace vessel 1, before it overflows into the convertervessel 3 via the weir 34. The metal melt 24 within the furnace vessel 1always has roughly the above-recited properties.

[0308] The melting and refining process within the furnace vessel 1proceeds continuously and is carried out in a quasi-stationary mannerwith very intensive mixing of the bath while continuously feeding thefollowing substances media and energies and under the following processconditions:

[0309] about 4.61 t/min preheated scrap 7 with a temperature of about834° C.,

[0310] liquid, FeO_(n)-rich, highly basic (CaO/SiO₂=3.55) and hotconverter slag 25 with a temperature of about 1620° C., which from the

[0311] converter vessel 3 counter to the direction of the metal flowflows into the furnace vessel 1 via the weir 34,

[0312] lime 14 (about 60% thereof in the form of blowing lime via thelime nozzles 35 and about 40% thereof in the form of lump lime via thecharging openings 11 arranged in the lid 4 of the furnace vessel 1, theratio blowing lime/lump lime can be modified as desired),

[0313] charging coal (lump coal) 13 via the charging openings 11provided in the lid 4 of the furnace vessel 1,

[0314] blowing coal (fine coal) 13 via the manipulator lances 32 and 23as well as via the coal sub-bath nozzles 33 of the furnace vessel 1,

[0315] natural gas 29 and gaseous oxygen 27 via the burners 32 a of thefurnace vessel 1,

[0316] N₂ 30 and natural gas 29 via the inert-gas bottom nozzles 33 ofthe furnace vessel 1,

[0317] gaseous oxygen 27 via the manipulator lances 32 and/or 23 of thefurnace vessel 1,

[0318] gaseous oxygen 27 via the afterburning lances 35 arranged in thelid 4 of the furnace vessel 1,

[0319] converter offgas 19 incl. dust in the converter offgas, streaminginto the furnace vessel 1 directly from the converter vessel 3,

[0320] false air, which is sucked into the furnace vessel 1 from theexternal surroundings, predominantly through the slag door 22 but alsovia openings for the electrodes arranged in the lid 4, as a result ofthe negative pressure prevailing in the furnace vessel 1,

[0321] blowing air 28 as conveying gas via the lances/nozzles 35, 32, 23and 33,

[0322] about 53.1 MW continuous electric energy input via the electrodes16 to satisfy the energy demand in the furnace vessel 1, which input atthe overall plant productivity of about 4.87 t crude steel/min (about292 t crude steel/operating hour) corresponds to an electric energyconsumption of about 181.6 kWh/t crude steel.

[0323] The products of the furnace vessel 1 are likewise withdrawncontinuously and in a semi-stationary manner, namely:

[0324] about 4.46 t/min pre-melt 24 rich in C and low in Si and havingthe above-recited properties, via the weir 34 in the direction of theconverter vessel 3,

[0325] about 416 kg/min slag 25 having the following properties: about12.2% FeO_(n) 0.46% P₂O₅ about 5.0% Fe_(met) 0.21% S 40.9% CaO basicity(CaO/SiO₂) = 2.0  7.8% MgO temperature˜1550° C.  5.8% MnO 20.4% SiO₂ 7.0% Al₂O₃

[0326] which leaves the plant continuously via the decanting part 2through the slag door 22,

[0327] about 522 Nm³/min offgas 19 and about 79.1 kg/min dust in theoffgas having the following properties Offgas (gaseous phase) Offgas(dust) 37.0 vol. % CO 72.5% FeO_(n) 23.1 vol % CO₂  9.0% CaO  3.3 vol. %H₂  3.4% SiO₂  8.4 vol. % H₂O  4.8% C 25.8 vol. % N₂  5.7% ZnO  1.7 vol.% O₂ balance = MgO + MnO + balance = Ar + SO₂ + F₂ Al₂O₃ + SnO₂ + P₂O₅total afterburning degree 43.9% temperature ˜ 1570° C. which pass fromthe furnace vessel 1 into the scrap preheating shaft 5.

[0328] After overflowing the weir 34, the pre-melt rich in C and low inSi passes into the converter vessel 3 continuously and at very intensivemovement of the bath mixes with the crude steel melt 24 which is alwayspresent in the converter vessel 3 and whose properties are continuouslycontrolled within close tolerances:

[0329] amount: about 90 t,

[0330] level of the metal bath in the converter vessel 3: about 0.5 mbelow the level of the weir 34,

[0331] composition (particularly the C content) and temperature equal tothe tapping values desired for the crude steel, in the present case asfollows:

[0332] C=0.05%

[0333] T=1620° C.

[0334] Within the converter vessel 3, above the crude steel melt 24,there collects the liquid converter slag 25, whose surface at a heightof the slag layer within the converter vessel 3 of about 1.8-2.0 m is upto 0.5-1.0 m higher than that within the furnace vessel 1 and which,hence, driven by gravity and by impulses from the movement of the bathinside the converter vessel 3, overflows continuously into the menacevessel 1 via the weir 34.

[0335] For the process control in the converter vessel 3 there henceresults the following task, which is accomplishedcontinuously/uninterrupted:

[0336] refining and heating the high-C, low-Si pre-melt flowing in fromthe furnace vessel 1 to the properties desired for the crude steel 24when tapping the same from the converter vessel 3 via the crude steeltapping opening 41 and at the same time mixing this partial stream ofthe metal melt with the metal bath 24 always present in the convertervessel 3, i.e. homogenization in the converter vessel 3 of the crudesteel melt 24 which flows out or is tapped via the tap opening 41,

[0337] carrying off the converter slag 25 and converter offgases 19arising continuously during the operation of the converter toward thefurnace vessel 1 and

[0338] adjusting conditions with respect to the quantity, compositionand temperature of the crude steel melt 24, slag 25 and offgases 19 inthe converter vessel 3, which remain roughly constant in the course oftime and which are adjusted to the required properties and the desiredtapping velocity of the crude steel 24 via the tap opening 41 (i.e. tothe desired plant productivity) and, again are controlled within certainboundaries by the crude steel tapping velocity and the refining velocityin the converter vessel 3.

[0339] In the case under consideration, the refining process in theconverter vessel 3 is conducted with very intensive mixing of the bath,in a quasi-stationary manner with continuous feeding of the followingsubstances, media and energies and under the following processconditions:

[0340] about 4.46 t/min high-C, low-Si pre-melt from the furnace vessel1, with the above-mentioned properties,

[0341] about 0.59 t/min fine scrap 12 as a cooling agent via thecharging openings 39 arranged in the converter lid 37, with thecomposition of the fine scrap 12 corresponding roughly to thecomposition of the mixed scrap as set forth in Table I and the max.piece length ≦amounting to 100 mm,

[0342] lump lime 14, quartzite and lump coal 13 likewise via thecharging openings 39 in the converter lid 37,

[0343] gaseous oxygen 27 via the water-cooled converter lance 35′,

[0344] gaseous oxygen 27 via the afterburning lances 35 and

[0345] N₂ 30 and natural gas 29 via the bottom flushing nozzles 36 ofthe converter vessel 3

[0346] The products of the converter vessel 3 are likewise withdrawncontinuously and in a semi-stationary manner, namely:

[0347] about 4.87 t/min (=about 292 t/h) crude steel 24 with theproperties 0.05% C about 620 ppm O dissolved 0.14% Mn about 30 ppm Ntraces of Si ≦1.5 ppm H 0.026% S T = 1620° C. 0.0038% P 0.21% Cu

[0348] via the tap opening 41 in the converter vessel 3,

[0349] FeO_(n)-rich, highly basic, liquid converter slag 2, having theproperties about 25.0% FeO_(n) 0.27% P₂O₅ about 5.0% Fe_(met) 0.21% S42.0% CaO basicity (CaO/SiO₂) = 3.55  7.9% MgO temperature˜1620° C. 4.8% MnO 11.8% SiO₂  2.9% Al₂O₃

[0350] via the weir 34 in the direction towards the furnace vessel 1 and

[0351] converter offgas 19 incl. dust in the converter offgas, with thefollowing properties: Offgas (gaseous phase) Offgas (dust) 84.0 vol. %CO 91.2% FeO_(n)  9.3 vol. % CO₂  3.5% CaO  3.0 vol. % H₂  0.7% SiO₂ 1.4 vol. % H₂O  0.8% C  0.6 vol. % N₂  1.7% ZnO  1.2 vol. % O₂ balance= MgO + MnO + Al₂O₃ + SnO₂ + balance = Ar + SO₂ + F₂ P₂O₅

[0352] total afterburning degree 11.0%

[0353] temperature 1620° C.

[0354] which from the converter vessel 3 pass directly into the furnacevessel 1.

[0355] Important process variables for the process course in the furnacevessel 1 and in the converter vessel 3 are given in the following Table:Process variable (input/output) Unit Furnace vessel 1 Converter vessel3 1. Flow rate metal t/min 4.61/4.46 4.46/4.87 slag kg/min 416 offgasNm³/min 522 2. Amount metal t about 90 about 90 slag t about 10 about 153. Retention time metal min about 20.2 about 18.5 slag min about 24about 119 4. Temperature metal ° C.  834/1550 1550/1620 slag ° C.1620/1550   −/1620 offgas ° C. 1620/1570   −/1620 5. Slag parametersFeO_(n)-content % about 25.0/about −/about 25.0 12.2 basicity (CaO/SiO₂)— 3.55/2.0    −/3.55 6. Offgas parameters degree of % 43.9 11.0afterburning (total CO—H₂) dust content g/Nm³ about 152 7. Metallicyield* % 96.8 96.4 8. Decarburization % C./min 0.070 0.110 velocity

Exemplary Embodiment 2

[0356] The charge mix consists of

[0357] 40% steel scrap

[0358] 30% sponge iron (pellets) and

[0359] 30% liquid pig iron

[0360] having the properties presented in Table II.

[0361] In the instant case, there is principally no essential differencecompared with the Exemplary embodiment 1 presented above as far as theplant configuration and the fundamental process course to be employedare concerned. Differences with respect to plant configuration andprocess control result from the different quantitative ratios andproperties of the components in the charge mix. The process is likewisecarried out using the plant variant according to FIG. 1, yet

[0362] employing the scrap preheating shaft 5 having the small effectivecross-section of about 5 m², wherein the difference with respect to thescrap preheating shaft 5 having the large effective cross-section ofabout 11.5 m² is made up for by providing an additional lid piece in thelid 4 of the furnace vessel 1, which piece matches the preheating shaft5 having the smaller effective cross-section. The additional lid piece(not illustrated) is configured identically with the lid 4 of thefurnace vessel 1 and in the case of using the shaft 5 of small effectivecross-section is firmly interlocked with the same, so that a gas-tightunit is formed,

[0363] as well as employing only one of the two scrap conveying belts 3for transporting, preheating (within the framework of the same heatingpart 9 already described) and charging the scrap 7 into the scrappreheating shaft 5 that has the small effective cross-section, i.e. isactive, wherein in the heating part 9 only that half of the, in all, tennatural gas/oxygen/air combination burners/lances 10 are operated whichare located above the active scrap conveying belt 8, while the secondhalf of the heating part 9 (behind the refractory dam already mentioned)and the second scrap conveying belt 8 remain passive, i.e. are not beingoperated.

[0364] Further differences compared with the Exemplary embodiment 1 liein the fact that in the present case there is continuous supply into thefurnace vessel 1 of liquid pig iron 20 via the pig iron chute 21 and ofsponge-iron pellets 12 via the charging openings 11. Sponge-iron pellets12 are charged to the converter vessel 3 as a cooling agent, namely inan amount of about 8.8% of the charge mix, i.e. about 29.3% of thesponge-iron pellets comprised in the charge mix, whose total portion inthe charge mix is 30%.

[0365] The total amount of the scrap in the charge mix is charged ontothe scrap conveying belt 8 by means of scrap charging cranes and afterpreheating in the heating part 9 and in the preheating shaft 5 iscontinuously supplied into or molten in the furnace vessel 1. The meanheight of the scrap column 7 in the preheating shaft 5 is 2.5 m. As theheat source for preheating of the scrap 7 in the heating part 9 and inthe preheating shaft 5 there serve the physical and the chemical heat,partial afterburning of the offgases 19 from the furnace vessel 1 andheat from a partial oxidation of the scrap during preheating.

[0366] The partial afterburning of the offgases 19 in the preheatingshaft 5 is carried out in two steps, with cold air 28 and gaseous oxygen27 being blown in continuously through the eight afterburning nozzles 47arranged in two planes, in a ratio of volumes of about air/O₂˜3.7. Inthe heating part 9 preheating is carried out stepwise, along the onehalf that has the active scrap conveying belt 8, by continuous blowingin of cold air 28 and gaseous oxygen 27 via the—in all—five combinedburners/lances 10 arranged in the lid of the heating part 9, which aredisposed above the active scrap conveying belt 8.

[0367] Important process variables for the process course in the heatingpart 9 and in the preheating shaft 5 are given in the following table:Process variables (input/output) Unit Heating part 9 Preheating shaft5 1. Scrap parameters flow rate* t/min 2.1 2.2 amount t about 5.94 about9.41 retention time min about 2.8 about 4.4 temperature ° C.  25/379 379/1057 oxidation % 0.47 2.42 2. Offgas parameters flow rate Nm³/min574/760 452**/574 temperature ° C. 1302/1086 1571**/1302 degree ofafterburning % 68.3/88.1 38.5**/68.3 (total CO—H₂) dust content g/Nm³about 46.5 about 48.3 3. Metallic yield*** % 99.6 103.3

[0368] Continuous melting of the scrap 7 preheated in the heating part 9and in the preheating shaft 5 is carried out in the furnace vessel 1while likewise continuously feeding the liquid pig iron 20 via the pigiron chute 21 and about 70.7% of the sponge-iron pellets 12 comprised inthe charge mix via the charging openings 11. The forming metal melt 24is at the same time carburized to a low-Si, high-C melt and partiallyrefined in the furnace vessel 1. The metal melt prior to overflowinginto the converter vessel 3 via the weir 34 exhibits the followingproperties: 1.69% C about 1550° C. 0.14% Mn liquidus temperature about1413° C. ≦0.05% Si  0.025% S 0.008% P

[0369] The metal melt 24 in the furnace vessel 1 has roughly theabove-mentioned properties throughout the entire process.

[0370] The melting and refining process in the furnace vessel 1 isconducted continuously and at very intensive mixing of the bath in aquasi-stationary manner while continuously feeding the followingsubstances, media and energies and under the following processconditions:

[0371] about 2.19 t/min preheated scrap 7 with a temperature of about1057° C. via the shaft 5,

[0372] about 1.60 t/min liquid pig iron 20 having properties inaccordance with Table II via the pig iron chute 21,

[0373] 1.13 t/min sponge-iron pellets 12 having properties as set forthin Table II via the charging openings 11,

[0374] FeO_(n)-rich, highly basic (CaO/SiO₂=3.55), liquid and hotconverter slag 25 with a temperature of about 1620° C., which from theconverter vessel 3 counter to the direction of metal flow flows into thefurnace vessel 1 via the weir 34,

[0375] lime 14 (about 60% thereof in the form of blowing lime via thelime nozzles 35 and about 40% thereof in the form of lump lime via thecharging openings 11 provided in the lid 4 of the furnace vessel 1, theblowing lime/lump lime ratio can be modified as desired),

[0376] blowing coal (fine coal) 13 via a manipulator lance 32 or 33 aswell as via the coal sub-bath nozzles 33 in the furnace vessel 1,

[0377] natural gas 29 and gaseous oxygen 27 via three burners 32 a ofthe furnace vessel 1,

[0378] N₂ 30 and natural gas 29 via the inert-gas bottom nozzles 33 ofthe furnace vessel 1,

[0379] gaseous oxygen 27 via the manipulator lances 32 and/or 23 of thefurnace vessel 1,

[0380] gaseous oxygen 27 via the afterburning lances 35 in the lid 4 ofthe furnace vessel 1,

[0381] converter offgas 19 incl. dust in the converter offgas, whichfrom the converter vessel 3 flow directly into the furnace vessel 1,

[0382] false air (not illustrated in FIG. 1), which is sucked into thefurnace vessel 1 predominantly through the slag door 22 but also via theopenings for the electrodes in the lid 4 from the external surroundingsas a consequence of the negative pressure prevailing in the furnacevessel 1,

[0383] blowing air 28 as conveying gas via the lances/nozzles 35, 32, 23and 33 and

[0384] about 53.2 MW continuous electric energy input via the electrodes16 for covering the heat demand in the furnace vessel 1, which input inthe present case at the overall plant productivity of about 4.94 t crudesteel/min (about 296 t crude steel/operating hour) corresponds to anelectric energy consumption of about 179.6 kWh/t crude steel.

[0385] The products of the furnace vessel 1 are likewise withdrawncontinuously and in a semi-stationary manner, namely:

[0386] about 4.67 t/min high-C, low-Si pre-melt 24 with the aboverecited properties via the weir 34 in the direction of the convertervessel 3,

[0387] about 428 kg/min slag 25 having the following properties about12.4% FeO_(n) 0.87% P₂O₅ about 5.0% Fe_(met) 0.16% S 42.1% CaO basicity(CaO/SiO₂) = 2.0  7.3% MgO temperature˜1550° C.,  4.4% MnO 21.0% SiO₂ 6.8% Al₂O₃

[0388] which exits the plant continuously via the decanting part 2through the slag door 22,

[0389] about 452 Nm³/min offgas 19 and about 79.8 kg/min dust in theoffgas having the following properties Offgas (gaseous phase) Offgas(dust) 40.7 vol. % CO 79.7% FeO_(n) 25.5 vol % CO₂  9.4% CaO  1.4 vol. %H₂  3.5% SiO₂  3.6 vol. % H₂O  1.4% C 26.5 vol. % N₂  2.0% ZnO  1.7 vol.% O₂ balance = MgO + MnO + Al₂O₃ + SnO₂ + balance = Ar + SO₂ + F₂ P₂O₅

[0390] total degree of afterburning 40.9%

[0391] temperature˜1570° C.,

[0392] which from the furnace vessel 1 pass into the scrap preheatingshaft 5.

[0393] After overflowing the weir 34, the pre-melt 24 rich in C and poorin Si passes into the converter vessel 3 continuously and at a meanvelocity of 4.67 t/min and mixes at very intensive movement of the bathwith the crude steel melt 24 which is always present in the convertervessel 3 and whose properties are continuously controlled within closetolerances:

[0394] amount: about 90 t,

[0395] level of the metal bath within the converter vessel 3: about 0.5m below the level of the weir 34,

[0396] composition (in particular the content of C) and temperatureequal to the tapping values desired for the crude steel, in the presentcase as follows:

[0397] C=0.05%

[0398] T=1620° C.

[0399] Above the crude steel melt 24 inside the converter vessel 3 therecollects the liquid converter slag 25, whose surface in the case of aslag layer height in the converter vessel 3 of about 1.8-2.0 m islocated up to 0.5-1.0 m higher than in the furnace vessel 1 and whichconsequently, driven by gravity and impulses from the movement of thebath in the converter vessel 3, overflows into the furnace vessel 1continuously via the weir 34.

[0400] In the instant case, the task to be accomplished by thecontinuous process control in the converter vessel 3 is the same as withthe Exemplary embodiment 1.

[0401] The refining process takes place within the converter vessel 3 ina quasi-stationary manner at very intensive mixing of the bath whilecontinuously feeding the following substances, media and energies andunder the following process conditions:

[0402] about 4.67 t/min pre-melt 24 high in C and low in Si and with theabove-mentioned properties from the furnace vessel 1,

[0403] about 0.47 t/min sponge-iron pellets 12 as the cooling agent viathe charging openings 39 of the converter lid 37, the properties of thesponge-iron pellets 12 being presented in Table II,

[0404] lump lime 14, quartzite and lump coal 13 likewise through thecharging openings 39 of the converter lid 37,

[0405] gaseous oxygen 27 via the water-cooled converter lance 35′,

[0406] gaseous oxygen 27 via the afterburning lance 35 and

[0407] nitrogen 30 and natural gas 29 via the bottom flushing nozzles 36of the converter vessel 3.

[0408] The products of the converter vessel 3 are likewise carried offcontinuously and in a semi-stationary manner, namely

[0409] about 4.94 t/min (=about 296 t/h) crude steel 24 with theproperties 0.05% C about 620 ppm O dissolved 0.08% Mn about 30 ppm Ntraces of Si ≦1.5 ppm H 0.022% S T = 1620° C. 0.0038% P 0.08% Cn

[0410] via the tap opening 41 of the converter vessel 3,

[0411] highly basic, liquid converter slag 25 rich in FeO_(n) and havingthe properties about 25.0% FeO_(n) 0.28% P₂O₅ about 5.0% Fe_(met) 0.145%S 41.9% CaO basicity (CaO/SiO₂) = 3.55 8.4% MgO temperature˜1620° C.2.6% MnO 11.8% SiO₂ 4.8% Al₂O₃

[0412] via the weir 34 in the direction of the furnace vessel 1 and

[0413] converter offgas 19 incl. dust of the converter offgas having thefollowing properties Offgas (gaseous phase) Offgas (dust) 84.8 vol. % CO93.1% FeO_(n)  9.4 vol. % CO₂  3.5% CaO  2.3 vol. % H₂  0.7% SiO₂  1.1vol. % H₂O  0.7% C  0.5 vol. % N₂  0.3% ZnO  1.3 vol. % O₂ balance =MgO + MnO + Al₂O₃ + SnO₂ + P₂O₅

[0414] balance=Ar+SO₂+F₂

[0415] total degree of afterburning 10.8%

[0416] temperature˜1620° C.,

[0417] which from the converter vessel 3 pass directly into the furnacevessel 1.

[0418] Important process variables for the process course in the furnacevessel 1 and in the converter vessel 3 are given in the following table:Process variable converter vessel (input/output) unit furnace vessel 13 1. Flow rate metal t/min 2.19*/4.67 4.67/4.94 slag kg/min 428 offgasNm³/min 452 2. Amount metal t about 90 about 90 slag t about 10 about 153. Retention time metal min about 19.3 about 18.2 slag min about 23.4about 117 4. Temperature metal ° C. 1057*/1550  1550/1620 slag ° C.1620/1550   −/1620 offgas ° C. 1620/1570   −/1620 5. Slag parametersFeO_(n)-content % 25.0/12.4   −/25.0 basicity (CaO/SiO₂) — 3.55/2.0   −/3.55 6. Offgas parameters degree of afterburning % 40.9 10.8 (totalCO + H₂) dust content g/Nm³ about 176 7. Metallic yield** % 95.2 96.1 8.Decarburization % C/mm 0.065 0.110 velocity

Exemplary Embodiment 3

[0419] The charge mix consists of

[0420] 50% sponge-iron pellets and

[0421] 50% liquid pig iron

[0422] having the properties given in Table II. In this case, the plantvariant according to FIGS. 3 and 4 serves for carrying out the process.Due to the fact that no scrap is contained in the charge mix, neither aheating part 9 nor a preheating shaft are needed. The fundamentalprocess course is very similar to that of Exemplary embodiment 2;differences with respect to plant configuration and process controlmainly concern the furnace vessel 1, provided that in the present case

[0423] the scrap preheating shaft 5 is replaced with a conventionalwater-cooled furnace elbow as the connection piece between the furnacevessel 1 and a hot gas duct (not illustrated in FIG. 3), as is nowcustomary with all conventional electric arc furnaces,

[0424] the five natural gas/oxygen burners 32 a in the furnace vessel 1are not operated as burners and are protected from damages either bybeing kept clear by means of air until they are needed again or areoptionally (not, however, in the present case) used as additionalafterburning nozzles 32 a in addition to the afterburning lances 35already provided in the lid 4 of the furnace vessel 1, and

[0425] provided that in terms of offgas characteristics (temperature,degree of afterburning, dust content etc.) there is no essentialdifference between this plant and process variant and the conventionalelectric arc furnace, i.e., that the physical and chemical heat of theoffgases 19 from the furnace vessel 1 remains largely unutilized and thedust content in the offgas 19 is comparable to that of the conventionalelectric arc furnace.

[0426] In the present case, about 24% of the sponge-iron pellets 12comprised in the charge mix, i.e. about 12% of the total charge mix, arecharged into the converter vessel 3 continuously as a cooling agent. Theresidual amount (principal amount) of the components of the charge-mixis likewise charged to the furnace vessel 1 continuously, namely

[0427] the liquid pig iron 20 via the pig iron chute 21 and

[0428] about 76% of the sponge-iron pellets 12 comprised in the chargemix via the charging openings 11.

[0429] The metal melt 24 which forms under supply of electric energy inthe furnace vessel 1 is at the same time carburized (with very limitedsupply of coal) to a low-Si and high-C melt and partially refined, sothat prior to overflowing into the converter vessel 3 via the weir 34that melt has the following properties: 1.98% C. about 1550° C. 0.10% Mnliquidus temperature about 1394° C. ≦0.05% Si  0.023% S 0.009% P

[0430] The metal melt 24 in the furnace vessel 1 has roughly theabove-listed properties throughout the entire process.

[0431] The melting and refining process in the furnace vessel 1 proceedscontinuously and is carried out at very intensive mixing of the bath ina quasi-stationary manner under continuous supply of the followingsubstances, media and energies and under the following processconditions:

[0432] about 2.56 t/min liquid pig iron 20 having properties inaccordance with Table II, via the pig iron chute 21,

[0433] about 1.94 t/min sponge-iron pellets 12 having properties inaccordance with Table II, via the charging openings 11,

[0434] liquid, FeO_(n)-rich, highly basic (CaO/SiO₂=3.53) and hotconverter slag 25 with a temperature of about 1620° C., which from theconverter vessel 3 flows into the furnace vessel 1 via the weir 34,counter to the direction of the metal flow,

[0435] lime 14 and dolomite 14 (about 60% thereof as blowing lime orblowing dolomite via the lime nozzles 35 and about 40% thereof as lumplime or lump dolomite 14 via the charging openings 11 arranged in thelid 4 of the furnace vessel 1, the ratio blowing material/lump materialcan be modified as desired),

[0436] blowing coal (fine coal) 13 via one or several of the manipulatorlances 32, 33 and/or the coal sub-bath nozzles 33 of the furnace vessel1,

[0437] nitrogen 30 and natural gas 29 via the inert-gas bottom nozzles33 of the furnace vessel 1,

[0438] gaseous oxygen 27 via the manipulator lances 32 and 23 of thefurnace vessel 1,

[0439] gaseous oxygen 27 via the afterburning lances 35 arranged in thelid 4 of the furnace vessel 1,

[0440] converter offgas 19 incl. dust in the converter offgas, whichflow into the furnace vessel 1 directly from the converter vessel 3,

[0441] false air (not illustrated in FIG. 3), which mainly through theslag door 22 but also via the electrode openings provided in the lid 4is sucked into the furnace vessel 1 from the external surroundings dueto the negative pressure that prevails in the furnace vessel 1,

[0442] blowing air 28 as a conveying gas via the lances/nozzles 35, 32,23 and 33,

[0443] about 53.2 MW continuous electric energy input via the electrodes16 for covering the heat demand in the furnace vessel 1, which input inthe present case at the overall plant productivity of about 4.67 t crudesteel/min (about 280 t crude steel/operating hour) corresponds to anelectric energy consumption of about 190.0 kWh/t crude steel.

[0444] The products of the furnace vessel 1 are likewise carried offcontinuously and in a semi-stationary manner, namely:

[0445] about 4.27 t/min high-C, low-Si pre-melt 24 with theabove-mentioned properties via the weir 34 into the converter vessel 3,

[0446] about 415 kg/min slag 25 with the following properties about12.0% FeO_(n) 1.13% P₂O₅ about 5.0% Fe_(met) 0.15% S 43.1% CaO basicity(CaO/SiO₂) = 2.0  7.2% MgO temperature˜1550° C.,  3.1% MnO 21.5% SiO₂ 6.7% Al₂O₃

[0447] which exits the plant continuously through the slag door 22 viathe decanting part 2 and

[0448] about 500 Nm³/min offgas 19 and about 74.7 kg/min dust in theoffgas with the following properties Offgas (gaseous phase) Offgas(dust) 50.9 vol. % CO 82.2% FeO_(n) 21.8 vol. % CO₂ 10.0% CaO  1.0 vol.% H₂  3.7% SiO₂  1.6 vol. % H₂O  0.7% C 22.8 vol. % N₂ balance = MgO +MnO + Al₂O₃ + P₂O₅  1.5 vol. % O₂ balance = Ar + SO₂ + F₂

[0449] total degree of afterburning 31.2%

[0450] temperature 1545° C.,

[0451] which from the furnace vessel 1 via the furnace elbow pass intothe hot gas duct of an offgas treating plant.

[0452] After overflowing the weir 34, the high-C, low-Si pre-melt 24passes into the converter vessel 3 continuously, at a mean velocity of4.27 t/min, and at very intensive movement of the bath mixes with thecrude steel melt 24 which is always present in the converter vessel 3and whose properties are continuously controlled within closetolerances:

[0453] amount: about 90 t,

[0454] level of the metal bath in the converter vessel 3: about 0.5 mbelow the level of the weir 34,

[0455] composition (in particular the content of C) and temperatureequal to the tapping values desired for the crude steel, in the presentcase as follows:

[0456] C=0.05%

[0457] T=1620° C.

[0458] Above the crude steel melt 24 inside the converter vessel 3 therecollects the liquid converter slag 25, whose surface in the case of aslag layer height in the converter vessel 3 of about 1.8-2.0 m islocated up to 0.5-1.0 m higher than in the furnace vessel 1 and whichconsequently, driven by gravity and impulses from the movement of thebath in the converter vessel 3, overflows into the furnace vessel 1continuously via the weir 34.

[0459] In this case, too, the task to be accomplished by the continuousprocess control in the converter vessel 3 is the same as with theExemplary embodiments 1 and 2.

[0460] The refining process is carried out in the converter vessel 3with very intensive mixing of the bath in a quasi-stationary mannerunder continuous supply of the following substances, media and energiesand under the following process conditions:

[0461] about 4.27 t/min high-C, low-Si pre-melt 24 with theabove-mentioned properties from the furnace vessel 1,

[0462] about 0.62 t/min sponge-iron pellets 12 as cooling agent throughthe charging openings 39 of the converter lid 37, the properties of thesponge-iron pellets 12 being presented in Table II,

[0463] lump lime 14 and lump coal 13 also via the charging openings 39of the converter lid

[0464] gaseous oxygen 27 via the water-cooled converter lance 35,

[0465] gaseous oxygen 27 via the afterburning lances 35.

[0466] nitrogen 30 and natural gas 29 via the bottom flushing nozzles 36of the converter vessel 3,

[0467] The products of the converter vessel 3 are likewise withdrawncontinuously and in a semi-stationary manner, namely:

[0468] about 4.67 t/min (=about 280 t/h) crude steel 24 with theproperties 0.05% C about 620 ppm O dissolved 0.05% Mn about 30 ppm Ntraces of Si ≦1.5 ppm H 0.021% S T = 1620° C. 0.0038% O

[0469] via the tap opening 41 of the converter vessel 3,

[0470] highly basic, liquid converter slag 25 rich in FeO_(n) and havingthe properties about 25.0% FeO_(n) 0.30% P₂O₅ about 5.0% Fe_(met) 0.13%S 42.4% CaO basicity (CaO/SiO₂) = 3.53  7.8% MgO temperature˜1620° C. 1.7% MnO 12.0% SiO₂  5.6% Al₂O₃

[0471] via the weir 34 in the direction towards the furnace vessel 1 and

[0472] converter offgas 19 incl. dust in the converter offgas, with thefollowing properties Offgas (gaseous phase) Offgas (dust) 79.6 vol. % CO92.8% FeO_(n) 14.1 vol. % CO₂  4.1% CaO  2.1 vol. % H₂  0.9% SiO₂  1.6vol. % H₂O  1.0% C  0.4 vol. % N₂ balance = MgO + MnO + Al₂O₃ + P₂O₅ 1.6 vol. % O₂ balance = Ar + SO₂ + F₂

[0473] total degree of afterburning 16.1%

[0474] temperature˜1635° C.,

[0475] which from the converter vessel 3 pass directly into the furnacevessel 1.

[0476] Important process variables for the process course in the furnacevessel 1 and in the converter vessel 3 are given in the following table:Process variables Converter (input/output) Unit Furnace vessel 1 vessel3 1. Flow rate metal t/min 2.56*/4.27  4.27/4.67 slag kg/min 415 offgasNm³/min 500 2. Amount metal t about 90 about 90 slag t about 10 about 153. Retention time metal min about 21.1 19.3 slag min about 29.8 about104 4. Temperature metal ° C. 1320*/1550  1550/1620 slag ° C. 1620/1550  −/1620 offgas ° C. 1635/1545   −/1635 5. Slag parametersFeO_(n)-content % 25.0/12.0   −/25.0 basicity (CaO/SiO₂) — 3.53/2.0  −/3.53 degree of afterburning % 31.2 16.1 (total CO + H₂) dust contentg/Nm³ about 150 7. Metallic yield** % 94.9 95.5 8. Decarburization %C./min 0.090 0.125 velocity

[0477] Important process parameters for and the productivity achievablein the exemplary embodiments presented above can be seen from Table V,whereas Table VI gives a summery of the consumption figures for theproduction of 1 t crude steel using the process and plant variants ofthe invention. TABLE V Process parameters and productivity for theExemplary embodiments 1 to 3 Exemplary embodiment No. 1 2 3 charge mixpig iron liquid wt. % — 30 50 steel scrap wt. % 100 40 — DRI pellets wt.% — 30 50 Reference parameters unit process parameters and productivityminimum required MVA 69.5 69.7 69.7 transformer output min 12.3 12.112.8 process parameter tap-to-tap time min 12.3 12.1 12.8 power-on-timefurnace vessel min continuously continuously continuously O₂ blowingtime min continuously continuously continuously mean refining rate inthe % C./min 0.070 0.065 0.090 furnace vessel mean refining rate in the% C./min 0.110 0.110 0.125 converter vessel tapping temperature of the °C. 1620 1620 1620 steel tapping temperature of the ° C. 1550 1550 1550slag offgas temperature at entry ° C. 812 1086 1545 into the hot gasduct O₂ in the offgas at entry into vol. % 5.1 3.8 1.5 the hot gas ductdegree of CO afterburning at % 97.6 88.1 30.0 entry into the hot gasduct degree of CO—H₂ % 97.6 88.6 31.1 afterburning at entry into the hotgas duct productivity net man days per year days/year 300.0 300.0 300.0(exchange vessel) output per minute t/min 4.87 4.94 4.67 output per hourt/hour 292.2 296.4 280.2 output per day t/day 7012.8 7113.6 6724.8output per year t/year 2103840 2134080 2017440

[0478] TABLE VI Consumption figures for Exemplary embodiments 1 to 3:Exemplary embodiment No. 1 2 3 charge mix pig iron, liquid wt. % — 30 50steel scrap wt. % 100 40 — DRI pellets wt. % — 30 50 type of consumptiontype unit amount consumed, unit/t crude steel metallic chargingsubstances liquid pig iron liquid t 0.323 0.548 steel scrap (mix) solidt 1.058 0.430 DRI/HBI pellets t 0.323 0.548 nonmetallic chargingsubstances lime lumpy kg 29.88 33.20 36.04 dolomite lumpy kg 0.00 0.000.88 quartzite lumpy kg 0.91 10.34 0.00 refractories bricks kg 2.9513.00 2.97 refractories gunning kg 0.73 0.75 0.74 material graphiteelectrodes graphite kg 1.23 1.06 0.94 media O₂ (lances + sub-bathgaseous Nm³ 31.16 28.89 39.19 nozzles) O₂ (burners + super-bath gaseousNm³ 21.12 16.70 7.52 nozzles) N₂ (bottom flushing) gaseous Nm³ 0.31 0.280.26 compressed air blowing air Nm³ 6.92 3.31 1.94 false air +ventilator air suction air - Nm³ 163.57 98.31 28.51 blowing air energysources electric energy kWh 181.6 179.6 190.0 natural gas Nm³ 3.70 1.280.26 charging coal lumpy kg 12.32 3.70 5.20 blowing coal fine-grained kg20.53 8.40 4.28 measurements, samples temperature probes pcs. 0.0170.017 0.017 sampling probes (metal) pcs. 0.033 0.033 0.033 CELOS probes(aO, T) pcs. 0.017 0.017 0.017 operating personnel man year 16.0 16.016.0 products crude steel t 1.000 1.000 1.000 slag kg 85.47 86.65 88.84offgas condensed kg 11.18 10.22 16.00 substances offgas gases Nm³ 228.08153.90 106.98

[0479] Apart from the production of crude steel, the plant concept whichhas been set forth, namely the variant without a preheating shaft 5 andwithout a heating part 9, can also be used for pretreating metal meltswith or without an iron content, wherein, in special cases, it wouldeven be conceivable to operate with negative pressure (f.i. as low as0.1 bar residual pressure in the whole vessel).

Exemplary Embodiment 4

[0480] Pretreatment of liquid pig iron, namely desiliconization,dephosphorization and desulphurization, which according to the inventionproceeds as follows:

[0481] continuous feeding of liquid pig iron (f.i. directly from the hotmetal chute of a blast furnace or a melt reduction plant or from anintermediate vessel) having the following properties: T = 1440° C.(blast furnace) 4.3 % C 0.6 % Si 0.5 % Mn 0.100 % P 0.040 % S

[0482] continuous prefining and optionally preheating by means ofelectric energy in the furnace vessel 1 with production of a low-Siintermediate product having the properties 4.0-4.1 % C T 1300-1400° C.≦0.10 % Si (adjustable as required) 0.4-0.5 % Mn 0.060-0.080 % P0.030-0.035 % S

[0483] continuous final refining of the low-Si intermediate product inthe converter vessel 3 and, if necessary, heating (through partialdecarburization) to pretreated pig iron with the properties 3.5-4.0 % CT = 1350-1400° C. ≦0.05  % Si 0.3-0.4 % Mn ≦0.020 % P ≦0.025 % S

[0484] The pig iron so pre-treated is tapped off from the convertervessel 3 continuously (f.i. into a subsequently connected intermediatevessel) or discontinuously into an intermediate vessel or into pig ironladles) and later-on is charged either to a converter or to an electricarc furnace or is cast into pigs at a casting machine.

[0485] During the process course there are continuously supplied bothinto the furnace vessel 1 and into the converter vessel 3

[0486] oxygen in the form of gaseous oxygen (lances, nozzles) and/oroxygen in the form of Fe ore, Mn ore, scales, dried FeO_(n)-rich sludgeetc. via lances, nozzles or via charging chutes and

[0487] slagformers (lime, fluorspar etc.), preferably in the form oflumps and optionally

[0488] carbon carriers (coal, coke, etc.) as well as

[0489] inert gas (No) as bottom flushing agent,

[0490] so that the process parameters, such as temperature control, slagcontrol (basicity about 3.0-3.5 in the converter vessel 3 about 1.8-2 inthe furnace vessel 1), mixing of the bath and quantitative ratiosmetal/slag, that are necessary for achieving the desired results can beadjusted in the converter vessel and in the furnace vessel.

[0491] Since the demand for electric energy in the exemplary embodimentset forth above is low (5-10 kW/t pig iron) at an equal temperature ofthe pre-treated pig iron being charged, in only a weak transformer of 20MVA is provided for the furnace vessel 1 at a plant productivity of 10t/min liquid pig iron (=600 t/h). In most cases encountered in actualpractice (pig iron with P≦0.200%), the electrodes in the furnace vessel1 can be omitted.

[0492] With appropriate process control, the process course set forthabove can also be effectively employed for pretreating special pig ironhaving a high content of V, Ti, Mn and P. Yet, the process, respectivelythe plant, is also very well suited to the production of liquid pig ironhaving a very low content of accompanying elements (Si, Mn, P and S atthe same time), i.e. for producing a pig iron melt of the “SORE PETAL”type from conventional pig iron.

Exemplary Embodiment 5

[0493] Further, the application of the process and plant is explained bymeans of an example for the production of a high-Cr and high-Ni pre-meltfor the production of stainless steel by subsequent VOD treatment. Theprocess course in accordance with the invention is as follows:

[0494] In a plant according to FIGS. 1 and 2, the solid chargingsubstances 7, consisting of

[0495] unalloyed and/or alloyed-steel scrap

[0496] FeCrHc, FeMo

[0497] Ni metal and/or FeNi

[0498] ore, f.i. chromium, nickel, manganese, molybdenum, etc. ores,

[0499] by means of the conveyor belt 8 are charged into the preheatingshaft 5 or into the electric arc furnace vessel 1 continuously via theheating part 9 and in doing so are preheated. Where liquid chargingsubstances 20, such as f.i.

[0500] pig iron, preferably pre-dephosphorized pig iron (% P≦0.025),and/or

[0501] liquid FeCrHSC (from an electric arc furnace or an inductionfurnace) are employed, such substances are introduced into the electricarc furnace vessel 1 continuously via the charging chute 21.

[0502] The melting process in the electric arc furnace vessel 1 iscarried out continuously with very intensive mixing of the bath, underthe following conditions:

[0503] continuous supply of gaseous oxygen 27 and inert gas 30 (N₂Ar)via nozzles 33, with the O₂/N₂/Ar ratio being adjustable as desired,

[0504] continuous supply of gaseous oxygen 27 via lances 23, 32, and

[0505] continuous supply of slagformers 14, such as burnt lime, burntdolomite, fluorspar etc. —in lumpy form through the charging openings 11and/or in fine-grained form via the nozzles 33 and/or lances 23, 32.

[0506] The object of the process control in the electric arc furnacevessel 1 is the quasi-stationary adjustment of predetermined processparameters, which in the case of producing a pre-melt for austeniticsteel quality 304 are as follows:

[0507] the metal melt 24 has properties which remain roughly constant atall times and lie within the tolerances 1.5-2.0 % C (depending on thecharge mix) T = 1620-1630° C. 0.2 % Si 0.5 % Mn 17.0-18.5 % Cr about 6.5% Ni

[0508] liquid slag 25 of a composition remaining roughly constant at alltimes, f.i. as a standard analysis 48 % CaO balance = MnO, Al₂O₃ etc. 31% SiO₂ (depending on the charge mix) ≦5 % MgO ≦4 % Cr₂O₃ ≦2 % FeO_(n)

[0509] which leaves the plant continuously through the slag door 22 viathe decanting part 2.

[0510] During operation, the metal melt 24 possessing the above-listedproperties flows continuously from the electric arc furnace vessel 1 viathe weir 34 into the converter vessel 3 and at very intensive movementof the bath mixes with the crude steel melt 24 which is always presentin the converter vessel 3 and which in the present case constitutes apre-melt for the next VOD treatment and in the converter vessel 3 isalways maintained at the composition and temperature

[0511] about 0.25% C

[0512] about 1700-1710° C.

[0513] desired for tapping.

[0514] The refining process (mainly decarburization) is carried out inthe converter vessel 3 under the following process conditions:

[0515] continuous feeding of gaseous oxygen 27 and inert gas 30 (N₂Ar)via the nozzles 36, wherein the ratio O₂/N₂/Ar is adjustable as desired;in the present case, the top-lance 35′ is not employed, the preferreddecarburization rate is 0.03-0.05% C/min,

[0516] temperature of the metal bath 24 from 1700-1710° C.,

[0517] continuous supply of charge-mix components as cooling andalloying agents 12—Ni and/or FeNi, low-Si FeCrHC and/or FeMnHC etc.

[0518] continuous supply of slagformers 14, such as burnt lime, burntdolomite, fluorspar etc. preferably in lumpy form via the chargingopenings 39, optionally also in fine-grained form via the nozzles 36,

[0519] formation/accumulation of an almost solid slag 25 of acomposition which remains roughly constant, f.i. as a standard analysisabout 30% CaO 2-5% Al₂O₃ ≦5% CaF₂ ≦15% SiO₂ ≦5% FeO_(n) 13-17% Cr₂O₃about 10% Fe_(met)  5-8% MgO ≦4% Cr_(met)

[0520] The metal product 24—a pre-melt of the above properties forsubsequent VOD treatment—is tapped from the converter vessel 3 via themetal tapping means 41. Tapping of the metal may be continuous ordiscontinuous without interrupting the process course in the electricarc furnace vessel 1.

[0521] The offgases 19 forming in the converter vessel 3 and in theelectric arc furnace vessel 1 are concertedly withdrawn via thepreheating shaft 5 and the heating part 9 and at the same time areemployed for preheating the solid charging substances 7. At the sametime, the charge in the preheating shaft 5 acts as pre-filter withrespect to the dust content in the offgas 19.

[0522] To avoid excessive accumulation of slag 25 in the convertervessel 3 or to avoid skulls being caused thereby, a so-called“washing-out operation” is carried out after about 3 hours of operationin that f.i. slightly higher amounts of FeSi, lime and fluorspar areintroduced into the converter vessel 3. This operation renders itpossible to liquefy the slag 25 in the converter vessel 3 and at thesame time reduce the content of Cr₂O₃, so that the slag 25 can pass intothe neighboring electric arc furnace vessel 1 over the weir 34 incountercurrent movement to the metal 24 without difficulty, and thatwithout causing high losses of Cr, before mixing with the slag portionformed in the electric arc furnace vessel 1. The so-called washing-outoperation can be carried out without incurring specific expenses andwithout substantially throttling the productivity both with the plantbeing operated with continuous tapping and with discontinuous tapping ofthe metal 24 from the converter vessel 3.

[0523] The process of the invention can also be employed for producingstainless qualities of low C content (≦0.05%), i.e. without a VOD plant.In this case, deoxidation and desulphurization of the steel like in themaking of C steel take place during the tapping from the convertervessel 3 and the subsequent secondary metallurgical treatment (f.i. at aladle furnace or a flushing station).

[0524] Essential advantages of the process of the invention as comparedto known, discontinuous processes for the production of stainlessqualities are:

[0525] substantially increased process and plant productivity

[0526] safeguarding of optimized slag control and high decarburizationefficiency

[0527] savings in terms of reduction silicon, slagformers and energysources—(C carriers and/or electric energy)

[0528] reduction in terms of power consumption

What is claimed is:
 1. A process for the production of metal melts,comprising the steps of: producing a pre-melt in an electric arc furnacevessel and bringing the pre-melt to a predetermined temperature leveland a predetermined chemical composition, continuously flowing thepre-melt into an oxygen-blowing converter vessel via an overflow weir,continuously refining the pre-melt in the oxygen-blowing convertervessel and carrying off the refined melt from the oxygen-blowingconverter vessel, and forming slag in the oxygen-blowing convertervessel in counterflow to the flow into the electric arc furnace vessel,from which the slag is withdrawn.
 2. A process according to claim 1,wherein the metal melt has a chemical composition and a temperaturewhich are adjusted in the oxygen-blowing vessel in a continuous mannerwhich corresponds to the chemical composition and temperature of thefinal melt or of the end product desired for tapping.
 3. A processaccording to claim 1, wherein offgases formed in the oxygen-blowingconverter vessel are withdrawn via the electric arc furnace vessel, withCO+H₂-afterburning being carried out both in the oxygen-blowingconverter vessel and in the electric arc furnace vessel.
 4. A processaccording to claim 1, wherein offgases arising in the electric arcfurnace vessel and offgases flowing over into the electric arc furnacevessel from the oxygen-blowing converter vessel are employed forpreheating lumpy charge material charged into the electric arc furnacevessel.
 5. A process according to claim 4, wherein the offgases employedfor preheating are afterburned during the preheating process.
 6. Aprocess according to claim 1, wherein a negative pressure is maintainedin the electric arc furnace vessel and in the oxygen-blower convertervessel.
 7. A process for the production of pig iron melts from ametallic charge mix, comprising the steps of: charging a pig iron inliquid form to an electric arc furnace vessel and bringing the pig ironto a predetermined temperature level, lowering Si- and P-contents in theelectric arc furnace vessel, flowing the liquid pig iron continuouslyinto an oxygen-blowing converter vessel via an overflow weir, partiallyrefining the liquid pig iron in a continuous manner in theoxygen-blowing converter vessel, drawing off the partial refined pigiron from the oxygen-blowing converter vessel, and flowing slag formedin the oxygen-blowing converter vessel in a counterflow direction to themetal into the electric arc furnace vessel, from which it is withdrawn.8. A process according to claim 7, wherein the metallic charge mix isformed from at least one of the following components: (a) scrap, such assteel scrap, solid pig iron, or cast iron, or mixtures thereof, (b)direct reduced iron in the form of pellets and/or briquettes and/or ironcarbide, and (c) liquid pig iron.
 9. A process according to claim 7,wherein, after predetermined process times, a liquefying or reductiontreatment, respectively, of the slag is carried out in theoxygen-blowing converter vessel.